# Proceedings of the Royal Society of London. Series B, Containing papers of a Biological character. Royal Society (Great Britain)

Online ISSN: 0080-4649
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Article
The nitromethylene heterocyclic compound 2(nitromethylene)tetrahydro)1,3-thiazine (NMTHT) inhibits the binding of [125I]alpha-bungarotoxin to membranes prepared from cockroach (Periplaneta americana) nerve cord and fish (Torpedo californica) electric organ. Electrophysiological studies on the cockroach fast coxal depressor motorneuron (Df) reveal a dose-dependent depolarization in response to bath-applied NMTHT. Responses to ionophoretic application of NMTHT onto the cell-body membrane of motorneuron Df are suppressed by bath-applied mecamylamine (1.0 x 10(-4) M) and alpha-bungarotoxin (1.0 x 10(-7) M). These findings, together with the detection of a reversal potential close to that estimated for acetylcholine, provide evidence for an agonist action of this nitromethylene on an insect neuronal nicotinic acetylcholine receptor. The binding of [3H]H12-histrionicotoxin to Torpedo membranes was enhanced in the presence of NMTHT indicating an agonist action at this vertebrate peripheral nicotinic acetylcholine receptor. NMTHT is ineffective in radioligand binding assays for rat brain GABAA receptors, rat brain L-glutamate receptors and insect (Musca domestica) L-glutamate receptors. Partial block of rat brain muscarinic acetylcholine receptors is detected at millimolar concentrations of NMTHT. Thus nitromethylenes appear to exhibit selectivity for acetylcholine receptors and exhibit an agonist action at nicotinic acetylcholine receptors.

Article
Injection of inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4) into voltage-clamped oocytes of Xenopus laevis elicited an oscillatory chloride membrane current. This response did not depend upon extracellular calcium, because it could be produced in calcium-free solution and after addition of cobalt to block calcium channels in the surface membrane. However, it was abolished after intracellular loading with the calcium chelating agent EGTA, indicating a dependence upon intracellular calcium. The mean dose of Ins(1,3,4,5)P4 required to elicit a threshold current was 4 x 10(-14) mol. In comparison, inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) gave a similar oscillatory current with doses of about one twentieth as big. Hyperpolarization of the oocyte membrane during activation by Ins(1,3,4,5)P4 elicited a transient inward current, as a result of the opening of calcium-dependent chloride channels subsequent to the entry of external calcium. In some oocytes the injection of Ins(1,3,4,5)P4 was itself sufficient to allow the generation of the transient inward current, whereas in others a prior injection of Ins(1,4,5)P3 was required. We conclude that Ins(1,3,4,5)P4 causes the release of intracellular calcium from stores in the oocyte, albeit with less potency than Ins(1,4,5)P3. In addition, Ins(1,3,4,5)P4 activates voltage-sensitive calcium channels in the surface membrane, via a process that may require 'priming' by Ins(1,4,5)P3.

Article
The biosynthesis in vivo of a number of amino acids, sugars, and purines in Paracoccus denitrificans grown on either [2,3-13C]succinate or [1,4-13C]succinate was investigated by using gas chromatography-mass spectrometry. The distribution of label in the TCA-cycle-related amino acids indicated that carbon intermediates of energy metabolism were utilized as precursors for the biosynthesis of these amino acids in vivo. The biosynthesis of glycine, serine, phenylalanine and glycerol from labelled succinate in vivo were consistent with phosphoenol pyruvate as an intermediate. A mechanism for the formation of C4, C5 and C6 sugars without the use of fructose-1,6-bisphosphate aldolase (which has not been detected in P. denitrificans) is proposed. The 13C-enrichments of ribose in the bacterium indicate that there are at least three routes of ribose biosynthesis operating during growth on labelled succinate. The probability distribution of labelled purine molecules was successfully predicted for adenine, guanine and adenosine, thus confirming their generally accepted route of biosynthesis in vivo.

Article
The metabolism of Paracoccus denitrificans, grown on either [2,3-13C]succinate or [1,4-13C]succinate, was investigated by using gas chromatography-mass spectrometry. The distribution of label in a group of metabolites closely related to the TCA-cycle intermediates showed that the flux of carbon from succinate in energy metabolism in vivo was via pyruvate (malic enzyme) and acetyl CoA. The labelling pattern of the carboxyl groups showed that one fifth of the succinate pool was formed by the regeneration of succinate via the TCA cycle, and four fifths was supplied externally as substrate from the medium.

Article
Paracoccus denitrificans was grown on either [2,3-13C]succinate or [1,4-13C]succinate, and extracts were analysed by using gas chromatography-mass spectrometry. The distribution of label in isoleucine indicated that the 2-ketobutyrate required for isoleucine biosynthesis was mainly produced from pyruvate by 2-keto-acid chain elongation (i.e. the 'pyruvate elongation pathway'). Approximately 10% of isoleucine was produced by a second pathway involving propionyl CoA. Threonine and glutamate were not utilized by P. denitrificans as a source of 2-ketobutyrate production for isoleucine biosynthesis under the growth conditions used.

Article
Injection of inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) into the animal pole of Xenopus oocytes induced membrane depolarization due to the internal mobilization of calcium, which activates a chloride conductance. Repetitive injections of Ins(1,4,5)P3 results in desensitization probably as a result of depletion of the internal store of calcium. Desensitization was restricted to the region surrounding the site of injection. Injection of Ins(1,4,5)P3 at one position induced desensitization, which failed to spread to a neighbouring region (ca. 200 microns away). Even when sufficient Ins(1,4,5)P3 was injected to induce calcium oscillations, there was still no evidence for the effects of Ins(1,4,5)P3 spreading to neighbouring regions. The fact that periodic calcium transients could also be established by the repetitive injection of small amounts of Ins(1,4,5)P3 suggests that calcium oscillations may also be localized. It is concluded that the Ins(1,4,5)P3-sensitive store of calcium comprises separate local compartments that can be activated independently of each other.

Article
The isolation of 1.6 S gamma -histone is described, its amino-acid composition recorded and an account given of some of its physicochemical properties. Its molecular weight has been calculated from sedimentation velocities to be 74 000 in its unaggregated condition. It thus represents a second histone of high molecular weight present in the nuclei of calf thymocytes. Both beta and 1.6 S gamma -histone are distinguished from the other four components in their ability to undergo aggregation. The gamma -histone, however, does not aggregate so readily or so extensively as does beta -histone. These two histones are also clearly distinguished by their amino-acid compositions.

Article
Many components of cell and nuclear size and mass are correlated with nuclear DNA content in plants, as also are the durations and rates of such developmental processes as mitosis and meiosis. It is suggested that the multiple effects of the mass of nuclear DNA which affect all cells and apply throughout the life of the plant can together determine the minimum generation time for each species. The durations of mitosis and of meiosis are both positively correlated with nuclear DNA content and, therefore, species with a short minimum generation time might be expected to have a shorter mean cell cycle time and mean meiotic duration, and a lower mean nuclear DNA content, than species with a long mean minimum generation time. In tests of this hypothesis, using data collated from the literature, it is shown that the mean cell cycle time and the mean meiotic duration in annual species is significantly shorter than in perennial species. Furthermore, the mean nuclear DNA content of annual species is significantly lower than for perennial species both in dicotyledons and monocotyledons. Ephemeral species have a significantly lower mean nuclear DNA content than annual species. Among perennial monocotyledons the mean nuclear DNA content of species which can complete a life cycle within one year (facultative perennials) is significantly lower than the mean nuclear DNA content of those which cannot (obligate perennials). However, the mean nuclear DNA content of facultative perennials does not differ significantly from the mean for annual species. It is suggested that the effects of nuclear DNA content on the duration of developmental processes are most obvious during its determinant stages, and that the largest effects of nuclear DNA mass are expressed at times when development is slowest, for instance, during meiosis or at low temperature. It has been suggested that DNA influences development in two ways, directly through its informational content, and indirectly by the physical-mechanical effects of its mass. The term 'nucleotype' is used to describe those conditions of the nucleus which effect the phenotype independently of the informational content of the DNA. It is suggested that cell cycle time, meiotic duration, and minimum generation time are determined by the nucleotype. In addition, it may be that satellite DNA is significant in its nucleotypic effects on developmental processes.

Article
A method for measuring oxygen uptake due to oil biodegradation for a long period, in a semi-closed system, with continuous nutrient replenishment is described. The rate and extent of degradation of Kuwait crude residues in the absence of high nutrient concentrations at 14 degrees C was measured, and related to the supply and uptake of inorganic nutrients. The rate controlling factor was the rate of replenishment of nitrogen as nitrate or ammonia. Approximately 26% (based on oxygen uptake) or 44% (based on oil recovery) of the oil was degraded, the difference probably being due to the production of soluble organic compounds. Some properties of the recovered oil were measured. The residues after partial degradation were of sufficient density to sink in seawater. It appears that at 14 degrees C, approximately 4 mu mol available nitrogen is required per milligram of oil oxidized (based on oxygen consumption). The capacity of sea water to degrade oil in the natural environment is tentatively discussed.

Article
Mastoparan, a 14-residue peptide, has been investigated with respect to its ability to form ion channels in planar lipid bilayers. In the presence of 0.3-3.0 microM mastoparan, two types of activity are seen. Type I activity is characterized by discrete channel openings, exhibiting multiple conductance levels in the range 15-700 pS. Type II activity is characterized by transient increases in bilayer conductance, up to a maximum of about 650 pS. Both type I and type II activities are voltage dependent. Channel activation occurs if the compartment containing mastoparan is held at a positive potential; channel inactivation if the same compartment is held at a negative potential. Channel formation is dependent on ionic strength; channel openings are only observed at KCl concentrations of 0.3 M or above. Furthermore, raising the concentration of KCl to 3.0 M stabilizes the open form of the channel. Mastoparan channels are weakly cation selective, PK/Cl approximately 2. A 12-residue analogue, des-Ile1,Asn2-mastoparan, preferentially forms type I channels. The ion channels formed by these short peptides may be modelled in terms of bundles of transmembrane alpha-helices.

Article
Analogues of 11-cis- and 9-cis-retinal with substitutions at positions 10 and 14 were used to regenerate analogue photopigments with two opsins: that of the transmuted (cone-like) 521-pigment of Gekko gekko and that of the rhodopsin of Porichthys notatus. The spectral absorbances and photosensitivities of the regenerated photopigments were determined and compared, first, between the two systems of analogue photopigments, and second, in the responses to the two opsins. Unlike the 10-fluoropigments, the comparable 14-compounds were significantly red-shifted by 19-30 nm and their sensitivity to light was similar to that of the parent 11-cis- and 9-cis-pigments. These were the results for both analogue pigments. In contrast, the 10-pigments were spectrally located close to the wavelengths of the parent compounds and the photosensitivity was significantly reduced, especially in the case of the 9-cis-analogues. Evidence was obtained for a steric hindrance effect at position 14, for no regeneration was obtained when methyl or ethyl groups were at this carbon. In the 10-substituted retinals, steric hindrance was noted only for the gecko; only the fluorosubstituted, but not the chloro-, the methyl- or the ethyl-substituted, retinals reacted. With the fish opsin, pigments were regenerated with all but the ethyl-substituted retinal. The gecko opsin appears to have a more restricted binding site. Another feature of the gecko was related to the chloride bathochromic and hyperchromic effects, in which the 521-pigment prepared in a chloride-deficient state has a blue-shifted spectrum compared with the spectrum obtained after the addition of chloride, and its extinction is raised by the addition of chloride to give a mean ratio of 1.23 for the two extinctions, one with, the other without, added chloride. The 11-cis-10-F-analogue pigment gave both chloride effects and the hyperchromic ratio was the same as that recorded for the native visual pigment. In contrast, the pigment formed with 11-cis-14-F-retinal gave a hyperchromic ratio significantly greater than 1.23. A similar contrast in the responses to chloride was obtained with the analogue photopigments regenerated with the 9-cis-10-F- and 9-cis-14-F-chromophores. This difference between the two systems is interpreted as the result of a specific configurational feature of the gecko opsin when in the chloride-deficient state that is relevant to the binding of the retinal analogue.(ABSTRACT TRUNCATED AT 400 WORDS)

Article
The traditional receptor-stimulus model of agonism began with a description of drug action based on the law of mass action and has developed by a series of modifications, each accounting for new experimental evidence. By contrast, in this paper an approach to modelling agonism is taken that begins with the observation that experimental agonist-concentration effect, E/[A], curves are commonly hyperbolic and develops using the deduction that the relation between occupancy and effect must be hyperbolic if the law of mass action applies at the agonist-receptor level. The result is a general model that explicitly describes agonism by three parameters: an agonist-receptor dissociation constant, KA; the total receptor concentration, [R0]; and a parameter, KE, defining the transduction of agonist-receptor complex, AR, into pharmacological effect. The ratio, [R0]/KE, described here as the 'transducer ratio', tau, is a logical definition for the efficacy of an agonist in a system. The model may be extended to account for non-hyperbolic E/[A] curves with no loss of meaning. Analysis shows that an explicit formulation of the traditional receptor-stimulus model is one particular form of the general model but that it is not the simplest. An alternative model is proposed, representing the cognitive and transducer functions of a receptor, that describes agonist action with one fewer parameter than the traditional model. In addition, this model provides a chemical definition of intrinsic efficacy making this parameter experimentally accessible in principle. The alternative models are compared and contrasted with regard to their practical and conceptual utilities in experimental pharmacology.

Article
When small electrolytic lesions area made in area 18 and [3H]proline is injected into area 17 of the same side, the inputs to the visual area of the superior temporal sulcus, from these two areas can be mapped separately and independently in the same animal. By using this approach, it was found that both area 17 and area 18 project to the same small region in the posterior bank of the superior temporal sulcus. We conclude that the latter area receives an overlapping input from area 17 and from area 18.

Article
Retrogradely transported tracers were injected into area 18 of the visual cortex of the adult cat to study the organization of corticocortical projections from area 17 to area 18. All injections, whether very small or relatively large, and irrespective of their exact location in area 18, produced a discontinuous, clustered distribution of labelled cells, mainly in layers II, III and upper IV, in a topographically related region of area 17. The mean centre-centre distance between neighbouring patches was about 750 microns. We conclude that the overall population of cells projecting to area 18 is genuinely distributed in a patchy fashion and that they provide an efficient spatial sample of information from area 17. Comparison of the dimensions of each injection site and of the retrogradely labelled territory suggested that each region in area 18 receives a convergent input from a zone in area 17 whose visual field representation is about 0.8 M-1 deg larger in all directions (where M is the magnification factor in millimetres per degree at the termination site in area 18). Pairs of injection were made in area 18 by placing small volumes of two fluorescent tracers, fast blue and diamidino yellow, side-by-side in either a rostrocaudal or a mediolateral plane, with different distances between them. When the boundaries of the dense central cores of two injection sites were separated, at their closest points, by about 1.6 mm, the two corresponding distributions of labelled cells in area 17 were just non-overlapping, suggesting that each group of cells in area 17 sends a divergent projection in innervate a zone about 0.8 mm larger in all directions in area 18. More closely spaced injections led to overlap of the distributions of labelling by the two dyes, with shared clusters containing a mixture of labelled cells. The proportion of double-labelled cells in these shared clusters never exceeded 4.4% (but was 70% after sequential injection of the two dyes at a single point). We conclude that, although each cluster of cells sends a divergent projection to area 18, the majority of individual axons terminate more discretely, perhaps providing specific inter-connections between functionally corresponding 'columns' in the two areas.

Article
The amplitudes of the responses of over 300 neurons in area 17 of the cat were examined as a function of the spatial frequency of moving sinusoidal gratings. The optimal spatial frequency and the bandwidth of the tuning curves were determined. The bandwidth varied considerably from neuron to neuron. Neurons optimally responsive to high spatial frequencies tended to have narrower tuning curves than those responsive to lower frequencies. Neurons with narrow spatial frequency tuning curves also tended to have narrow orientation tuning curves. These observations suggest that linear spatial summation tends to occur over a relatively constant area of visual field despite marked differences in each neuron's optimal spatial frequency, a prediction of one model of visual analysis. There was little difference in either the optimal spatial frequencies or the bandwidths of tuning for different functional classes of neuron. Neurons with broad tuning curves tended to be restricted to lamina IV and its environs, being concentrated in the deep part of lamina II-III and the upper part of lamina IV ab. Neurons with very low optimal spatial frequencies were uncommon and tended to be found either at the border of laminae II-III and IV or in lamina V. These laminar distributions are discussed with respect to the laminar differences in the projection of l.g.m. X- and Y-cells to the visual cortex.

Article
Considerable interest has been aroused by the use of the pentacyclic triterpene acid, icterogenin, in studies associated with bilirubin excretion and the genesis of icterus of the intrahepatic cholestasis type. This compound, which produces within a few hours after administration to sheep and rabbits a very marked decline in bile flow and the amount of bilirubin excreted hourly without any histological damage to the liver parenchyma visible in the ordinary light microscope, has proved to be very useful in the study of the South African ovine photosensitization disease known as 'geeldikkop' ('yellow thick head'). In connexion with research on this disease, a study of the relationship between the chemical structure of the pentacyclic triterpenes and their icterogenic activity is in progress. The first part of this work dealing with certain structural variations in triterpenes of the oleanane and 24-noroleanane (hedragane) series is reported in this paper. Assays are recorded of sixteen of these compounds and some of their derivatives for such activity, using a modification of the rabbit test described in the first paper of this series (Heikel, Knight, Rimington, Ritchie & Williams 1960). Four new icterogenic agents are discussed, namely: 22$\beta$-angeloyloxyoleanolic acid, 22$\beta$-angeloyloxyhedragolic acid, 22$\beta$-angeloyloxy-24-hydroxyoleanolic acid and 22$\beta$-angeloyloxy-24-oxo-oleanonic acid. The first two mentioned compounds are extremely active, their potency far surpassing that of icterogenin. Icterogenic activity of these acids appears, so far, to be based upon the presence of a $\beta$-equatorially orientated hydroxyl group at C(3) or a hydroxyl at C(24) and a 22$\beta$-angeloyl side-chain on the triterpene molecule. Stereoisomer specificity is shown in respect of icterogenicity by these compounds since the epimers of two of these substances carrying $\alpha$-axially orientated hydroxyls at C(3) have been shown to have no such effect on bile flow or bilirubin excretion. Removal of the angelic acid side-chain, substitution of the hydroxyl groups or replacement of these with a ketone function, is followed by loss of activity.

Article
A study has been made of the number and distribution of the Meynert cells in area 17 of the visual cortex in the macaque monkey. There are between 30 000 and 40 000 Meynert cells in one hemisphere and these are randomly distributed with an average uniform area density of about 25 cells per square millimetre. The area density of Meynert cells is similar in the representation of the fovea and the perifoveal cortex. These findings are discussed in relation to the basic uniformity of the functional architecture of the visual cortex.

Article
Previously reported work in this series (Brown, Rimington & Sawyer 1963) produced evidence that icterogenic activity (i.a.) of the pentacyclic triterpene acids is based upon the presence of a $\beta$-equatorially orientated hydroxyl group at C (3), or a hydroxyl at C (24), and a 22$\beta$-angeloyloxy side chain in the molecule of the particular active compound. The second part of this work, dealing with certain structural variations in triterpenes of the oleanane, 24-noroleanane (hedragane) and ursane series, is reported in this paper. These variations involve i.a. esterification of the C (28) carboxyl, saturation of the 22$\beta$-angeloyl side chain or replacement of this by simple saturated aliphatic acids. Assays are recorded of a further thirteen of these compounds for icterogenic activity using the modified technique described in the second paper of this series (Brown et al. 1963). It has been concluded from this work that the icterogenicity of 3$\beta$- or 24$\beta$-hydroxy triterpene acids is undoubtedly associated with the 22$\beta$-angeloyloxy side chain. Removal of the esterifying group at C (22) or its replacement by a simple saturated fatty acid residue is followed by complete loss of activity. Esterification of the C (28) carboxyl produces a considerable decrease in icterogenic potency due, probably, to a decrease in solubility of the compound.

Article
Evidence is presented for the synaptic connectivity between a physiologically characterized and intracellularly filled GABAergic interneuron and a corticotectal pyramidal neuron in area 17 of the cat visual cortex. The interneuron was located in layer 4 and had the morphological characteristics of a clutch cell. The physiological data demonstrated that the clutch cell received direct X-type innervation from the dorsal lateral geniculate nucleus. These results indicate that a GABAergic neuron is directly involved during the first cortical stages of geniculocorticotectal interactions. Furthermore, the proximal location of the clutch-cell inputs to the labelled dendrite suggests a strategic siting of intracortical feedforward inhibition.

Article
It has been suggested by Julesz & Pennington (1965) that certain types of composite stimulus may be memorized in a holographic rather than a photographic manner, It will here be pointed out that not only static but time-varying patterns can be stored in an analogous fashion, and the word 'holophone' is proposed for such a system, the theory of which is expounded in detail. If the memorization of short sequences does involve holophonic as opposed to gramophonic principles, then not only would the problem of content-addressing be automatically solved, but those parts of the brain which hold the memories in question should exhibit periodic response characteristics which might be directly accessible to neurophysiological study.

Article
The gene A protein of bacteriophage phi X 174 initiates replication of super-twisted RFI DNA by cleaving the viral (+) strand at the origin of replication and binding to the 5' end. Upon addition of E. coli rep protein (single-stranded DNA dependent ATPase), E. coli single-stranded DNA binding protein and ATP, complete unwinding of the two strands occurs. Electron microscopic analyses of intermediates in the reaction reveal that the unwinding occurs by movement of the 5' end into the duplex, displacing the viral strand in the form of a single-stranded loop. Since unwinding will not occur in the absence of either gene A protein or rep protein, it is presumed that the rep protein interacts to form a complex with the bound gene A protein. Single-stranded DNA binding protein facilitates the unwinding by binding to the exposed single-stranded DNA. Further addition of the four deoxyribotriphosphates and DNA polymerase III holoenzyme to the reaction results in synthesis of viral (+) single-stranded circles in amounts exceeding that of the input template. A model describing the role of gene A protein and rep protein in duplex DNA replication is presented and other properties of gene A protein discussed.

Article
Edmund (1960) has shown that in the dentitions of almost all non-mammalian vertebrates, teeth are replaced in waves which regularly sweep through alternate tooth positions. He explained the ontogeny of these patterns of tooth replacement in terms of biological units called Zahnreihen whose existence has been accepted by nearly all workers studying tooth replacement. In the present paper it is argued that there is no unequivocal evidence, either during development or in adult animals, that Zahnreihen have any biological significance. Reconstructions were made from serial sections of the developing dentitions in the lower jaws of 15 embryos of Lacerta vivipara. It was evident that Zahnreihen have no significance in this animal. Rudimentary teeth were produced with varying frequency in positions 3, 5, 6, 8, 10 and 13. Contrary to the predictions of all previous theories explaining the ontogeny of tooth development in reptiles it was in these apparently random positions that the first teeth were produced. Furthermore, apart from during the first few days of embryonic dental development, it was clear that the development of a row of alternating teeth was initiated in sequence from the back to the front of the jaw to be followed by a similar sequence of development of the intervening teeth. On the basis of this evidence a new model to explain the sequence of tooth initiation in reptiles is proposed. The following assumptions have been made. (A) Ectomesenchymal cells migrate anteriorly through the developing jaws initiating a reaction from the oral ectoderm. (B) The oral ectoderm develops competence to react to the ectomesenchyme in three stages. First it generates abortive clumps of ectodermal cells; second it becomes capable of inducing the adjacent ectomesenchymal cells to form dentine and third it becomes capable of laying down enamel. (C) At all times the dental lamina has the potential of taking part in tooth development according to the regional competence achieved. (D) Developing tooth germs produce a condition which inhibits tooth development around them. Using these assumptions it is possible to explain all stages in the development of the wave replacement of alternate teeth in L. vivipara. It is also possible to explain previous observations on the ontogeny of reptilian dentitions. The sphere of inhibition which surrounds developing teeth is particularly important because it ensures that developing teeth are evenly spaced through the jaw. It is argued that the wave replacement of alternate teeth is an automatic sequel to this and is of only secondary functional significance.

Article
1. Anthropometric and physiological data relevant to the capacity for exercise have been obtained in 46 healthy young adults, including 23 male and 20 female factory workers and three male athletes. 2. The measurements included maximal oxygen uptake on a cycle ergometer, cardiac frequency during submaximal exercise, total body potassium, the breadth of the limb muscles (at three sites), skinfold thickness at four sites, somatotype, forced vital capacity, transfer factor for the lung, total body haemoglobin, grip strength of the hand, vertical force during a standing jump and customary activity by questionnaire. 3. Linear regression relationships were obtained for: body potassium on thigh muscle, body weight and skinfold thickness (residual S.D. 6.4 g), maximal oxygen uptake on cardiac frequency and either body potassium or thigh muscle and forced vital capacity (residual S.D. 0.19 l min-1), oxygen uptake during cycling on rate of work and body weight (residual S.D. 0.09 l min-1) and maximal cardiac frequency on maximal oxygen uptake (residual S.D. 7.2 min-1). The coefficient and constant terms for men and women, with the exception of the coefficient terms for the description of body potassium, do not differ to a material extent.

Article
The eye is a clear zone eye with extensive movement of retinula cells on adaptation to light. The ommatidium has three types of rhabdomere, at different levels, so that the eye necessarily abstracts at least three kinds of information simultaneously from the incoming rays. In the light-adapted state light can enter each ommatidium only via a crystalline tract that is surrounded by dense pigment grains. A small distal rhabdomere (cell 7) always lies at the end of this tract. In the dark-adapted eye the retinula cell nuclei and distal rhabdomere move to the cone tip and the crystalline tract is drawn into the cone. There is then a region of the retinula cell column, between cone tip and proximal rhabdoms, across which there is no structure that could act as a light guide. A key question, therefore, is how the light is focused across this clear zone in the dark-adapted state. As shown by the wide angular distribution of eyeshine when a parallel beam is incident on the dark-adapted eye, rays are poorly focused upon the columns of the large rhabdoms. The wide visual fields of receptors 1-6 in the dark-adapted eye, inferred from the observation of eyeshine, are seen as a way of narrowing the bandwidth of spatial frequencies, so that only the largest objects in the visual field contribute to motion-detection. This would improve the signal-to-noise ratio, not in the receptors themselves, but in the neural mechanism, by simplifying the incoming signal.

Article
A form of recall is discussed in which some elements of an event serve to initiate recall of the whole set of elements which comprised an event. The conditions which enable learned associations between pairs of elements to be used for such recall are quantitatively assessed for recall procedures which use only direct associations from the initial elements ('simple recall') and which use both direct and indirect associations ('progressive recall'). The theory is equivalent to the analysis of a neural model in which randomly arranged excitatory connections between a set of cells can be strengthened by simultaneous activity in their presynaptic and postsynaptic elements. The problems involved in a direct neural implementation of the model are discussed, and it is seen that some of the mechanisms resemble known physiological mechanisms in the cerebral cortex. The relationship between recall and recognition learning is discussed and the evidence relating these functions to the hippocampal formation is assessed.

Article
The Copley Medal is awarded to Professor D. Keilin, for his fundamental researches in the fields of protozoology, entomology and the biochemistry of enzymes. Professor Keilin’s early work was on parasitic insects, and it contains much that of lasting value and some which is regarded as classic. He made brilliant studies in the anthomyid larvae, on viviparous reproduction in higher flies, and on inter-exes in the human louse.

Article
I am using the term gluconeogenesis in this lecture to denote any new formation of carbohydrate from non-carbohydrates. These non-carbohydrates include amino acids, as well as the lactate continuously produced in the body, e.g. in blood cells and in the exercised muscles. When lactate is the precursor of carbohydrate the formation of glucose from it constitutes a re-formation rather than a new formation as the lactate has been derived from glucose. But as the enzymic mechanisms of glucose formation from lactate and from amino acids are essentially the same, it is reasonable to treat them jointly. Gluconeogenesis is a biosynthetic process of major importance. I intend to review first some aspects of the physiological role of gluconeogenesis. This will lead to the fact that the amounts of carbohydrate which are synthesized vary within very wide limits—between almost nil and perhaps 200 g per day in the case of the human adult—and this will bring me to the main subject: the question of how the rate of gluconeogenesis is regulated and adjusted to changing needs.

Article
'I must say to you, as I’ve oft-times said already, that ’tis not my intention to stick stubbornly to my opinions, but as soon as people urge against them any reasonable objections, whereof I can form a just idea, I’ll give mine up, and go over to the other side.’ (A. van Leeuwenhoek: see Letter 81, 19 March 1694.) As these words of his testify, Antony van Leeuwenhoek had a very forthright and truly scientific attitude to controversy. Born 333 years ago this year, in the same year as John Locke, Christopher Wren and Jan Vermeer, there can have been few men, if indeed any in the history of science, whose observations and ideas were more in advance of the general knowledge of their times. In his hundreds of letters, over a period of fifty years to this Society, of which he was a Fellow, he unfolded the existence of a new and undreamt-of world of living creatures which ranged in size as far below the limit of unaided vision as the largest mammals extended above it. In fact, by his own computation, a thousand million of the smallest of his little creatures, the bacteria, were no bigger than a coarse grain of sand (Letter 33, to R. Hooke, 12 November 1680). Not only was he the first man to see bacteria, with lenses and microscopes made with his own hands, but he described virtually all the morphological varieties of bacteria that we recognize today. However, Leeuwenhoek’s lasting contributions to knowledge go far beyond his discovery of protozoa and bacteria. He carried out researches on red blood cells, which he accurately measured and often used as a standard of size; not only this, but he also observed their movement through the capillaries, thus completing the story of the circulation of the blood, established earlier by his contemporary, William Harvey. His comparative observations on his own spermatozoa and those of animals and his understanding of their role in procreation led him to speculate imaginatively, if somewhat wildly and erroneously, on the mechanism of fertilization and inheritance.

Article
Genes are made of nucleic acid. Enzymes are made of protein. The amino acid sequence of a particular protein is synthesized under instruction from a particular piece of nucleic acid. Each protein is made of one or more polypeptide chains, synthesized by condensing together amino acids, head to tail, with the elimination of water. A typical polypeptide chain is several hundred amino acid residues long. Nevertheless only twenty different kinds of amino acids are commonly found in proteins. This standard set of twenty is the same throughout nature. Nucleic acid is made of polynucleotide chains. The repeating unit of the chain is a sugar (ribose for RNA , deoxyribose for DNA ) connected to a phosphate. A base is joined on to each sugar. There are four common bases in nucleic acid. DNA usually has adenine, guanine, cytosine and thymine. In RNA thymine is replaced by uracil.

Article
A glance at previous Leeuwenhoek Lectures reveals that in a number of cases the Lecturer has felt obliged to preface his account with an apology to the effect that the subject of his lecture would seem to bear little relationship to the distinguished work of Antony van Leeuwenhoek. In my case, however, such apology is unnecessary as a reasonably direct connexion can be established between those remarkable observations in the seventeenth century and the work described here. Leeuwenhoek’s description of bacteria is based on their appearance under his primitive but remarkably effective microscopes. Such appearance is, of course, governed by shape and we see from the published record that cocci, bacilli and spirochaetes were observed and accurately described in terms of size and shape. These features are functions of the nature and rigidity of the wall surrounding the organisms and so are related to molecular structure; the purpose of my lecture is to describe certain aspects of the recently acquired knowledge of the molecular architecture of bacterial cell walls. The great interest that has developed in the chemistry and biochemistry of bacterial cell walls during the last ten years or so has arisen for a number of reasons (cf. Salton 1964). In the first place, walls are of interest because they represent a substantial proportion of the metabolic products of the cell; they frequently comprise up to 20% of the dry weight of cells and so must be regarded as important metabolites. Moreover, their chemical structure is interesting in view of their physical properties. Thus, besides being reasonably rigid structures with considerable strength they are nevertheless freely permeable towards cellular products and nutrients. Under certain conditions even large molecules such as antibodies, extracellular enzymes and nucleic acids can penetrate the wall, although the full extent and nature of this permeability, and the effect of negatively charged polymers (e. g. teichoic acids) in the wall, has not been clearly defined. The wall is frequently the site of important antigenic material; for example, in many cases it has been shown, that group- or type-specific antigens are located in the outer structures of the cell, including the wall. Consequently, a better understanding of the immunological properties of bacteria, and particularly such features as patho-genicity, require a full understanding of the structure, function and biosynthesis of wall components.

Article
Haemoglobin is the respiratory protein of the red blood cells which carries oxygen from the lungs to the tissues and facilitates, both directly and indirectly, the return transport of carbon dioxide. Mammalian haemoglobin has a molecular weight of 64500 and contains two pairs of polypeptide chains: the α -chains with 141 amino acid residues each and the β -chains with 146. Each chain is combined with one haem. Myoglobin, the oxygen carrier of muscle, is closely related to haemoglobin, but has a simpler constitution: it consists of only one polypeptide chain of 153 residues and a single haem. The amino acid sequences of the myoglobins and haemoglobins of man and of several animals have been determined (Dayhoff & Eck 1968). By means of the method of isomorphous replacement with heavy atoms, X-ray analysis of sperm whale myoglobin at 2·0 Å resolution provided the first solution of the structure of a protein (Kendrew et al . 1960; Watson 1969). All but 21 of its 153 residues form part of helices; over most of their length these helices have conformations closely resembling the right-handed α -helix of Pauling & Corey (1951). The chain is divided into 8 helical segments, separated by corners or non-helical regions. Together these form a kind of basket into which the haem group fits neatly, so that only its propionic acid side-chains protrude into the surrounding liquid (figures 1, 2). X-ray analysis at 5·5 Å resolution showed each chain of horse haemoglobin to be folded in much the same way as the single chain of sperm whale myoglobin. The 4 chains are arranged tetrahedrally, each carrying one haem in a pocket near the protein surface. The chemically identical halves of the molecule are related by a twofold symmetry axis (figure 3, plate 18; Cullis et al . 1962).

Article
It is exactly 40 years since Ferrier died, and 39 years since Sherrington gave the first Ferrier Lecture in honour of his work. Sherrington (1906) had dedicated The integrative action of the nervous system to Ferrier ‘in token of recognition of his many services to the experimental physiology of the central nervous system’. At Aberdeen Ferrier had been taught by Bain, the Professor of Logic, who kept a model of the human brain upon his lecture table. Ferrier moved to London in 1870, and was excited by Hughlings Jackson’s revolutionary discoveries and ideas about the nature and localization of the sensory and motor functions of the human brain. Early in 1873 he discussed Fritsch & Hitzig’s (1870) pioneer galvanic stimulations of the dog’s cortex with his friend James Crichton-Browne. In the spring and summer of that year he performed his pioneer faradic stimulations of the brains of monkeys in the laboratory of the West Riding Lunatic Asylum, of which Crichton-Browne was Medical Director (Sherrington 1928). He sought to ‘put to experimental proof the views entertained by Dr Hughlings Jackson on the pathology of Epilepsy, Chorea and Hemiplegia, by imitating artificially the "destroying" and “discharging lesions” of disease which his writings have defined and differentiated’ (Ferrier 1873). 'The phenomena of localized and unilateral convulsive movements, depending, as Hughlings Jackson shows, on vital irritation of certain regions of the cortex, are essentially of the same nature as those caused by electrisation of the same regions’ (1876, p. 133). But Ferrier believed that many of the movements he mapped by electrical stimulation had evidently a purposive or volitional character’ (1876, p. 163). In 1876 he transferred his monkey map to the brain of man, and described of the relation between brain fissures and bony landmarks; and in 1883 he suggested that the time had come when localized cerebral lesions should be excised by the surgeon. For this, as he later recalled with amusement, he was criticized in an editorial in the Lancet (Ferrier, 1888), but in 1884 Godlee removed a localized tumour ‘of the size of a walnut’ (Sherrington 1928) from the Rolandic cortex through an opening exactly overlying it and but little larger than itself. Ferrier and Hughlings Jackson both witnessed this memorable operation (Trotter 1934). As time went on, experimentalists interested themselves more in defining details of localization than in developing concepts of function (Phillips 1966). ‘More penetrative modes and aims of analysis came to be little pursued,’ wrote Sherrington (1928). ‘A localization vogue reigned for nearly a quarter of a century, and became in due course tedious and relatively infertile.’

Article
Coincident with the more spectacular developments in biology of the last two decades there has quietly emerged a new technology with far-reaching potential, namely the growth and manipulation of animal and plant cells in culture. It has naturally led to an emphasis on homogeneous populations of isolated cells as a step towards simplifying the formidable complexities of even the simplest multicellular tissues. In this way cell culture tends to make microbiologists of us all, followers in the footsteps of Anthony van Leeuwenhoek himself. The microbiological approach is highly productive in the present limited state of knowledge, but will be even more productive if the special properties of metazoan as opposed to protozoan cells can be preserved and analysed. Metazoan cells, in particular, are highly social, and many properties, which may be missed in cultures, are dependent on interactions between the cells. These may be either long range, mediated for example by hormones circulating widely in body fluids, but with high specificity for certain target cells, or short range, at nerve synapses for example, or in growth following wounds.

Article
French research on Latimeria published before 1972 is first briefly recalled. After the Anglo-Franco-American Expedition of 1972, the material obtained enabled us to focus attention on the histology of the kidney and ureter and on ultrastructural aspects of the postnatal gland. Ovarian eggs of unusual volume have been collected, measured and weighed. Kinematic analysis of the intracranial articulation was carried out in 1973 on a frozen coelacanth that reached Paris. Studies in 1974 of a 41 cm specimen, the smallest known at that time and estimated to be 3 1/2 years old, showed that the brain still filled the cranial cavity: thus, it is later that allometric growth of the cranial cavity relegates the brain to the posterior part of the skull. In the same specimen, radiographed after injection with colloidal barium oxide, we were able to specify the likely role of the contractile organs fused to the branchial arteries: they may serve to regulate arterial pressure in the head during sudden movements of the jaws, and thus of the anterior cranium, as prey is captured. Lastly, the structural characteristics of the teeth, scale denticles, and spines on the lepidotrichia have been revealed, as also has the lamellar structure of the scales, in which there is a crossed orientation of the fibres in the different layers.

Article
In the past, research on body temperature too often nearly became a branch of physics. A model from physics, the thermostat, was taken to explain the thermoregulatory functions of the anterior hypothalamus. A change occurred when simple methods became available for injecting drugs into the cerebral ventricles of unanaesthetized animals, and when intraventricular injections of noradrenaline and 5-hydroxytryptamine were found to affect temperature. These monoamines appear to exert a tonic influence on temperature by being released from monoaminergic neurons ending in the hypothalamus. But they are not the mediators of endotoxin fever. Nor are they essential for maintaining normal temperature. The mediators of endotoxin fever are E prostaglandins. They raise temperature when injected intraventricularly, appear during endotoxin and lipid A fever in cerebrospinal fluid, but disappear from it when fever is brought down by antipyretics which inhibit prostaglandin synthesis. Many bodily functions, other than temperature are kept constant. It is the 'milieu interieur' of Claude Bernard that is kept constant. A factor which apparently governs the 'milieu interieur' in the hypothalamus is the calcium ion concentration, since lack of calcium in the hypothalamus raises (and excess lowers) temperature.

Article
DNA, the chemical component of the gene, plays a central role in biology and contains the whole information for the development of an organism, coded in the form of sequences of the four nucleotide residues. The lecture describes the development and application of some methods that can be employed to deduce sequences in these very large molecules. Special attention has been applied to a rapid simple method in which DNA polymerase is primed with specific oligonucleotide primers, thus making it possible to study small sections of radioactively labelled DNA. The techniques have been applied to the single-stranded DNA of bacteriophage phi X 174, and two sequences of about 250 nucleotides long have been deduced and related to the amino acid sequences of the proteins for which they code.

Article
In 1958 Keilin gave the Leeuwenhoek Lecture and in it he described fairly extensively the observations that Leeuwenhoek had made of the dormant state among micro-organisms. There would be no point in going over this material; instead it will be useful to take up the story again in 1877. This was when Robert Koch wrote a classical paper on the work he had done with the rod-shaped bacteria that were known to cause anthrax. He developed a technique for culturing these in aqueous humour and he demonstrated clearly that the spore and the vegetative cell which differ enormously in size, appearance and staining properties are, in fact, interconvertible forms of the same organism (Koch 1877). In making this observation he had discovered the most primitive of life cycles and one which was subsequently found to occur in a variety of Gram-positive bacilli. From that time onwards bacterial spores have remained of interest for medical and veterinary reasons and also in the food preservation industry and in agriculture. More recently sporulation in bacilli has been studied as a developmental system that might be susceptible to analysis in terms of modern biochemistry. A considerable amount of work has now been done and it seems an appropriate moment to stop and enquire how successful these efforts have been.

Article
The author comments first on the probable role of cytoplasmic determinants throughout development and then on progress towards an understanding of their molecular basis. His view is that the cytoplasmic determinants of eggs, so clearly visible in some mosaic invertebrate eggs, are no different in principle from cytoplasmic control molecules which exist in all cells throughout development. There is extensive traffic of cytoplasmic proteins into the nuclei of adult cells, but as yet no proof that all cells possess gene-controlling substances in their cytoplasm. New cell-types almost always arise by division of other cells, and the asymmetric distribution of cytoplasmic determinants at cell division could account for consequent changes in gene activity and cell differentiation. The difference, then, between the development of a mosaic egg and the specialization of adult cells, would according to this view, lie in the extent of the asymmetrical distribution of cytoplasmic determinants, and not in their nature or mode of action. It is well known that some so-called 'regulative' species of eggs behave as if the cytoplasmic determinants are only poorly localized at the egg stage, but become more precisely distributed as development proceeds. In this respect regulative eggs may be compared to differentiating adult cells. The mechanism proposed here is one in which there is a continuing exchange of information between nucleus and cytoplasm, so that products of genes accumulate in the cytoplasm of a cell, and then re-enter the nucleus thereby determining which genes shall subsequently be active. Under unchanging conditions, genes would reprogramme their own activity. But at different times in development, there are extracellular influences which can cause environmental differences between two sides of a cell; such situations exist at sperm entry, during blastocel formation, and during embryonic induction, and could cause an asymmetrical distribution of intracellular cytoplasmic determinants. A partitioning of these determinants into two daughter cells would lead to changes in gene activity. This proposal is no more than a hypothesis, but has been specified here because it underlies a basic assumption made in much of the work described in this article, that an understanding of how gene activity is controlled in specialized cells will lead directly to an understanding of cytoplasmic determinants in eggs.

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