The Royal Society
0080-4622
2054-0280
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Visceral nociception: peripheral and central aspects of visceral nociceptive systems Discomfort and pain are the sensations most commonly evoked from viscera. Most nociceptive signals that originate from visceral organs reach the central nervous system (c.n.s.) via afferent fibres in sympathetic nerves, whereas parasympathetic nerves contain mainly those visceral afferent fibres concerned with the non-sensory aspects of visceral afferent function. Noxious stimulation of viscera activates a variety of specific and non-specific receptors, the vast majority of which are connected to unmyelinated afferent fibres. Studies on the mechanisms of visceral sensation can thus provide information on the more general functions of unmyelinated afferent fibres. Specific visceral nociceptors have been found in the heart, lungs, testes and biliary system, whereas noxious stimulation of the gastro-intestinal tract appears to be detected mainly by non-specific visceral receptors that use an intensity-encoding mechanism.
Tập 308 Số 1136 - Trang 325-337 - 1985
The polar transport of auxin and vein patterns in plants The hormone auxin is transported through many plant tissues with a definite velocity. It is thought that certain channels, or pumps, located at the basal ends of cells, are responsible for the hormone’s transport. It is also known that auxin will induce veins when applied to suitable tissues. T. Sachs has suggested that it is the flow of the hormone that induces vessels. He suggests that discrete strands form because the transport capacity of a pathway increases with the flux that that pathway carries, leading to a canalization of flow. I cast this in the form of a more specific hypothesis: I suppose the permeability for the transport of auxin through the basal plasmalemma of a cell (by means of whatever kind of pump or channel) to increase with flux. I then show that discrete veins will form provided that the transport permeability increases rapidly enough with flux, and provided that the movement of auxin is not too polar, in the sense that there is a substantial amount of diffusive movement of auxin in addition to polar transport. The same hypothesis offers an explanation for the loops of veins found under certain conditions.
Tập 295 Số 1078 - Trang 461-471 - 1981
Some life-history consequences of modular construction in plants The nature and life-history consequences of modular construction in plants are discussed with particular reference to growth, reproduction and survival. Plants grow by the iteration of modular units and as a consequence growth can be described in terms of the population dynamics of these structural units. Changes in size, whether positive or negative, depend on the birth and death rates of modules; however, if the births continue to exceed the deaths, plants then have the capability of attaining enormous sizes, especially if they are clonal. The population nature of plant growth also means that plants of the same age may show large variation in individual size if individuals differ in their relative growth rates. Correlations between age and size are often, therefore, very weak. Constraints on the allocation of resources accumulated during growth have important implications for the reproductive schedules of plants, but the analysis of constraint functions has so far revealed little about the actual detail of these schedules. All the meristems of semelparous plants are involved in or die at reproduction and as a consequence death of the genet follows reproduction. For iteroparous plants, however, there are fundamental differences between the reproductive schedules of plants with a single shoot module and those with many shoot modules. The former demonstrate a relatively constant rate of reproduction from year to year following maturity whereas the latter show a continual increase in fecundity with size and age. The reproductive schedules of clonal plants are further discussed in relation to the allocation of meristems to either growth or reproduction. The pattern of mortality is examined at both the level of the module and the genet. Particular attention is focused on the survival and senescence of leaves and shoots; there is no equivalent regular shedding of organs in unitary organisms. Whereas genet senescence and death are coincident with shoot module death in semelparous plants, there is no evident relation between them in iteroparous plants. The life span of the genet reflects the birth and death rates of its modules and both aclonal and clonal plants that are iteroparous may achieve considerable longevity. The longevity of aclonal plants often seems to be restricted by the accumulation of dead material and the problems of being large. Clonal plants are, in contrast, potentially immortal. It is questionable whether the genets of iteroparous plants show senescence as defined for unitary organisms since there is no separation of germ plasm from soma and since apical meristems do not appear to senesce. Insofar as they retain the capacity for rejuvenescence from apical meristems, genets of modular organisms do not senesce; it is only the constituent organs that show senescence, death and decay.
Tập 313 Số 1159 - Trang 31-51 - 1986
Modular growth in seed plants Modular growth in seed plants may be analysed in terms of three architectural elements: the unit of morphogenesis, the module and the architectural model. Some of the salient features of these structures are reviewed, compared and contrasted. A variety of plant shapes and sizes may be derived schematically from them by two sorts of transformation, gigantism and repetition. The former is uncommon in seed plants, but repetition produces a wide array of constructions. Repetition of the architectural model, a process known as reiteration, leads to a colonial structure characteristic of the crowns of many mature trees. This is often an expression of the plant’s opportunistic response to environmental variations in resource availability. The reiterated complexes formed as a result may show some characteristic ontogenetic and phylogenetic sequences to give an architectural continuum of construction.
Tập 313 Số 1159 - Trang 77-87 - 1986
Cytochrome oxidase patches: a new cytoarchitectonic feature of monkey visual cortex
In normal macaque monkeys a histochemical stain for cytochrome oxidase activity revealed a striking pattern of regularly spaced patches in primary visual (striate, area 17, V1) cortex. The patches were most obvious in layers II and III, but also in layers I, IV b, V and VI; only in layers IV c and IV a were they absent. The patches were oval shaped, about 250 by 150 pm and aligned into rows spaced about 350 pm apart. Along each row a patch was located about every 550 pm; often patches in neighbouring rows were aligned, creating a square array. T heir density was about one patch per 0.2 mm
2
(550 by 350 pm) in opercular cortex. The patches were also labelled preferentially by stains for lactate dehydrogenase, succinate dehydrogenase, acetylcholinesterase (AChE), and myelin. In V2, a coarser pattern of broad parallel stripes labelled by cytochrome oxidase, lactate dehydrogenase, and AChE was present. The cytochrome oxidase patches were absent in non-prim ate species like the cat, mink, tree shrew, mouse, rat, rabbit, and ground squirrel. However, they were present in all prim ate species examined, including the rhesus, cynomolgus, owl, and squirrel monkey, baboon, bushbaby, and hum an. While more species should be tested, it appears that the patches are a cytoarchitectonic feature unique to prim ate visual cortex. In the owl monkey patches of anterogradely transported horseradish peroxidase (HRP) were found in layers IV c
a
, III, and II after injection of the tracer into the lateral geniculate nucleus (l.g.n.). They coincided exactly with the position of patches in adjacent sections processed for cytochrome oxidase. A similar result was obtained in the macaque, except that patches were not present in layer IV c
a
. These experiments established that the cytochrome oxidase patches receive a direct, patchy projection from the lateral geniculate body. However, retrogradely filled layer VI cells in the owl monkey bore no regular relation to the patches. In the macaque, the ‘honeycomb’ of geniculate terminals in layer IV a matched a similar honeycomb pattern of cytochrome oxidase staining. In the Nissl stain three sublayers in layer IV a were identified: the honeycomb was located in layer IV a
p
. In V2, in the owl monkey the parallel stripes of enhanced cytochrome oxidase activity received a direct projection from l.g.n. or pulvinar. In the macaque, after intraocular injection of [
3
H]proline, the rows of patches in layers II and III lay in register with ocular dominance columns seen by transneuronal radioautography in layer IV c. In another macaque, one eye was removed and the cortex stained for cytochrome oxidase, AChE and Nissl substance after six months survival. In layer IV c light and dark bands corresponding to the ocular dominance columns were visible; surprisingly the dark cytochrome oxidase bands matched the light AChE and Nissl bands. The set of bands belonging to the missing eye was determined by examining cytochrome oxidase staining and proline radioautographs in another macaque that sustained severe eye injury by [
3
H]proline injection. In striate cortex, bands of radioactive label from the injured eye matched ocular dominance columns appearing more lightly stained by cytochrome oxidase. In the macaque tested six months after enucleation, in every other row the cytochrome oxidase patches appeared pale and shrunken. These lighter rows fit into precise register with the lighter ocular dominance columns in layer IV c, confirming the correspondence between rows of patches and ocular dominance columns demonstrated by proline injection. AChE staining of patches was similarly affected by eye removal. The effect of visual deprivation upon cytochrome oxidase staining was tested in two monocularly sutured macaques. In the l.g.n. no effect was detected. In visual cortex wide light columns alternating with thin dark columns were observed in layer IV. In one m acaque the ocular dominance columns were labelled independently by H R P injection into a deprived l.g.n. lamina. The H R P labelled ocular dominance columns fit within the pale cytochrome oxidase columns; this establishes that monocular deprivation causes a relatively greater loss of enzyme activity in ocular dom inance columns belonging to the closed eye. However, there was also loss of cytochrome oxidase staining along the borders of the normal eye dominance columns, indicating that ocular dominance columns in layer IV are subdivided into core zones flanked by border strips that are susceptible to loss of cytochrome oxidase activity with suture of either eye. The core zones are the same width as the rows of cytochrome oxidase patches and correspond to the dark bands seen in Liesegang stains of normal macaque striate cortex. In two adult cats the effect of monocular lid suture at 28 d old was assessed: no effect upon cytochrome oxidase staining in l.g.n. or cortex was observed. The optic disc representation in visual cortex was studied by 2-deoxyglucose radioautography and cytochrome oxidase staining after eye removal or lid suture in m acaque monkeys. It appeared as a pale oval, 1.65 times longer than the optic disc, a distortion probably required to m aintain overall isotrophy in magnification factor. Patches were present in the disc representation although ocular dominance columns are absent: they appeared rounder and more widely separated. In the temporal cresent patches were also present. They were larger, rounder, and less densely spaced than patches in binocular cortex. Deoxyglucose mapping in a macaque monkey monocularly stimulated with a display of parallel black and white stripes of irregular width and spacing rotated through all orientations has resulted in patches in the upper layers over ocular dominance columns corresponding to the open eye. These patches match cytochrome oxidase patches situated in every other row, thus suggesting that cells located in cytochrome oxidase patches respond to all orientations of stimulus. Macaques binocularly stimulated with vertical or horizontal stripes show a complicated pattern of deoxyglucose uptake, overlapping extensively with the pattern of cytochrome oxidase patches. In one monkey the right eye was removed and 18 d later the animal was stimulated with vertical stripes. Deoxyglucose radioautography and cytochrome oxidase staining combined in single tissue sections each revealed a matching pattern of ocular dominance columns in layer IV. In the upper layers, dots of radioautographic label were present, matching cytochrome oxidase patches in alternate rows. In foetal monkeys at E142-144 the laminar pattern of cytochrome oxidase staining in visual cortex was remarkable for a prominent wide band of intense activity in layer IV b and upper IV c
a
, absent in mature macaques. In tangential section, patches were visible in layers II, III and in layer IV b -IV c
a
, which indicates that patches form in monkey visual cortex before birth. The functional significance of the patches remains uncertain. It has been suggested that the visual field is analysed in visual cortex by small modules containing several hypercolumns of each stimulus variable. The cytochrome oxidase patches may constitute the anatomical correlate of these proposed modules.
Tập 304 Số 1119 - Trang 199-253 - 1984
Quantitative studies on tissue transplantation immunity IV. Induction of tolerance in newborn mice and studies on the phenomenon of runt disease A simple method for the induction of actively acquired tolerance of homologous tissues in newborn mice is described (§§2-1, 2-2 and 2-3). With some donor/recipient strain combinations a high proportion of mice injected intravenously with homologous tissue cells is rendered tolerant of skin grafts from animals of the donor strain (§§3-1, 3-4 and 3-5), provided that the cells are administered within 24 h of birth. As the age of the recipients increases, so the proportion of tolerant mice falls (§3-2); a ‘ eutral period’ in the life of the recipients lies between the latest age at which they can be rendered tolerant and the earliest age at which they can be rendered immune. The induction of tolerance is less effective when homologous cells are injected intraperitoneally into newborn mice, and (with our strains) wholly ineffective when they are injected subcutaneously (§3-3). Tolerance can be induced with spleen, bone marrow or thymus cells (§3-4), and abolished (‘adoptive immunization’) with sensitized spleen and thymus cells as well as with lymph node cells (§5-2). Further experiments on the specificity of tolerance are described (§5.1). In newborn rabbits, the intravenous inoculation of homologous spleen or thymus cells results in the induction of tolerance in only a small proportion of animals (§3-6). The injection of adult homologous lymphoid cells into newborn mice leads to the development of a syndrome described as runt disease because, in its extreme form, it is characterized by gross retardation in development (§3-5). Runt disease is marked by varying degrees of involution of the recipients’ lymph nodes, and by pathological changes in the spleen, liver and other organs (§3-7). In its acute form it is fatal, but when more mildly expressed it need not be a serious handicap (§3-5). Two possible causes of runt disease are considered and subjected to experimental test (§4). The theory that runt disease is infective in origin cannot be upheld (§4.1). O n the contrary, it is shown conclusively that runt disease is immunological in origin, and that it is the consequence of an immunological reaction of the homologous cells against the tissues of their hosts (§6-2). For (a) the injected homologous cells persist indefinitely in the tissues of their hosts (§3-8); (b) although the injection of Fxhybrid spleen cells into newborn mice of the parental strains is usually quite harm less (§4-3), the injection of parental strain cells into hybrid recipients is followed by the typical syndrome of runt disease (§4-6); (c) mice can be protected from runt disease if they receive, together with the homologous cells,adult isologous spleen cells (§4-4); (d) the severity and frequency of runt disease are enhanced if sensitized homologous spleen cells are injected—i.e. cells from donors already sensitized by host strain tissues (§4-5); (e) acute runt disease can be avoided by the injection of adult tissue cells containing no, or only a very small proportion of, immunologically competent cells (§§4-2, 6-3); and (f) the severity and incidence of runt disease are largely determined by antigenic differences between donor and host strains (§6-2). Finally (g) it is already known that embryonic cells, though adept in producing tolerance, fail altogether to produce runt disease (§6-3). Tolerance of homologous tissues can occur in the complete absence of runt disease and cannot therefore depend upon the lymphoid hypoplasia that accompanies it (§6-3). O n the other hand, runt disease frequently depends upon the induction of tolerance by the injected cells, which are therefore able to persist and to react against the tissues of the host over a relatively long period of time. W ith certain donor/recipient strain combinations in which runt disease is particularly violent and rapid in onset, the induction of complete tolerance need not be necessary (§6-3), the young hosts succumbing to the disease before their own defence mechanism has m atured sufficiently to destroy the cells that cause it. W ith some donor/recipient strain combinations, the susceptibility to runt disease of hybrid mice injected with spleen cells from mice of the parental strains falls off with increasing age (§ 4-6), despite the fact that with this experimental design even adult recipients may be expected to be ‘ tolerant ’ of the injected cells. Similarly, the injection of adult mice made tolerant at birth with large doses of donor strain spleen cells does not bring about an increase in the severity of the disease (§4‘7). The production of runt disease in a severe form seems therefore to depend upon the hosts’ own lymphoid organs being relatively undeveloped when confronted with foreign lymphoid cells. It has been shown by Simonsen that the splenomegaly produced in chickens injectedin ovo or soon after hatching with homologous spleen or blood cells is due to a ‘ graft-against-host ’ reaction (§6*2), and the same interpretation has been put upon the ‘secondary disease’ which often occurs in irradiated mice protected against the effects of radiation by adult homologous spleen or bone marrow cells (§6-4). These two phenomena and runt disease are therefore considered to have a common etiology. The occurrence of runt disease is a sensitive indicator of the presence of immunologically competent cells in the inocula used to induce tolerance. The finding that blood leucocytes and thymus cells can cause runt disease when injected into newborn mice (§4-2) suggests that at least some of the cells among them are capable of immunological reactivity. Bone marrow cells, whilst bringing about some degree of lymphoid hypoplasia, do not cause acute runt disease, and they may therefore be used conveniently for the induction of tolerance with those donor/recipient strain combinations in which the injection of spleen cells is always lethal. Certain clinical implications are discussed (§6-5). It is suggested that the possibility of ‘graft-against-host’ reactions and the occurrence of immunologically competent cells in adult blood should be borne in mind in the interpretation of haemolytic disease and in devising treatments of any kind which depend upon the transplantation of lymphoid cells.
Tập 242 Số 694 - Trang 439-477 - 1959
The separation of visual axes in apposition compound eyes
Measurements of the interommatidial angle (Δ
ϕ
) and facet diameter (
D
)
of the same ommatidia
in a number of insects and crustaceans with large eyes have been related to the effective intensity at which the eye functions by the following theory. The highest spatial frequency which the eye is able to reconstruct as a pattern is limited by the interommatidial angle Δ
ϕ
, Which is the sampling angle, because two ommatidia are required to cover each cycle of the pattern. At the same time, the absolute modutlation of light in the receptors caused by the pattern depends on three interdependent factors. (
a
) The theoretical minimum angular sensitivity function, which has a width of θ/
D
at the 50% level. The wavelength θ is taken as 0.5 μm. This component is not only the limiting angular resolving power of the lens: it reduces modulation caused by all patterns, with greater loss at higher spatial frequencies. Larger lenses increase resolution and sensitivity. (
b
) The effective light catching area of the rhabdom. This is the angular subtense of the rhabdom area (the receptor) as seen in the outside world (i.e. subtended through the posterior nodal point of the lens), and is the equivalent of the grain size in a film. Large receptors favour sensitivity at the expense of resolution. (
c
) The
F
value or focal ratio
f/D
, as in the camera, where
F
is the distance from the focal plane to the posterior nodal point. Larger
F
values increase sensitivity. The modulation resulting from these three factors is then set so that it exceeds the noise caused by the random arrival of photons at each ambient intensity. From this, the optimum value of the product
D
Δ
ϕ
(known as the eye parameter) can be calculated for eyes adapted to any ambient intensity. The same result is reached by a recent theory of Snyder, Stavenga & Laughlin (1977) who calculate the value of
D
Δ
ϕ
which allows the eye to reconstruct the maximum number of pictures despite photon noise. The eye parameter (divided by half the wavelength) is the ratio of the highest spatiai frequency passing the lens to the highest spatial frequency reconstructed by the eye. Compound eyes should have larger facets and interommatidial angles than predicted by diffraction theory alone because photon noise must be exceeded at all intensities. Theoretically,
D
Δ
ϕ
lies in the range 0.3 to 0.5 for bright light insects and is increased to 2.0 or more for those active in dim light. As well as depending on intensity,
D
Δ
ϕ
should depend on factors such as the typical angular velocity and level of intensity discrimination at which the eye is used. As
D
Δ
ϕ
can be measured from the outside of the eye, the theoretical predictions can be compared with measured values. Most of this paper consists of maps of the values of
D
Δ
ϕ
for eyes of a variety of arthropods from different habitats. The maps are made by a new convention in which the minimum theoretical field of each ommatidium is placed in angular coordinates as a circle of diameter θ/
D
with centre on the axis at the place where it lies on the eye. To do this, a value of θ must be assumed. Every fifth facet is taken on most maps with the fields magnified five times. The overlap or separation of these circles of diameter θ/
D
shows the local value of
D
Δ
ϕ
for any direction for each part of the eye. The method is independent of horizontal and vertical axes, of directions of facet rows, of regularity of facets and of eye radius. The problem of mapping a surface with double curvature upon a flat sheet was solved approximately by working with strips taken along the eye surface. Equal distances on the map then represent equal angles in any direction; with this projection there are no poles, and axes are arbitrary. Maps of
D
Δ
ϕ
reveal that compound eyes differ according to the intensity of light they normally encounter; eyes of animals which are active in bright light have smaller values of
D
Δ
ϕ
. The smallest value of about 0.3 is found in the forward facing acute zone of the sand wasp
Bembix
, which hovers while hunting in bright sunshine. The absolute limit set by diffraction of 0.25 (for square facets) is approached but never reached. Values of
D
Δ
ϕ
up to about 2.0 or even 4.0 are found in crepuscular animals which have apposition eyes. The interpretation is that the values of
D
and Δ
ϕ
are the result of a compromise between contrast sensitivity and resolution. An increase in aperture provides increased modulation and therefore increased sensitivity, but the additional angular resolving power which comes with the increased aperture is not used because sensitivity is also enhanced by an increase in the receptor size. The ommatidium then detects only the lower spatial frequencies (wider stripes) from the range which passes the lens. In an ommatidium optimized for any but the highest known intensities, both Δ
ϕ
and
D
(and therefore
D
Δ
ϕ
) are larger than they would have to be if set at the diffraction limit. The maps also reveal that many apposition compound eyes have one or more regions of smaller Δ
ϕ
, called acute zones. None of the eyes are spherically symmetrical; all have gradients of both
D
and Δ
ϕ
, and all have regions where Δ
ϕ
varies in different directions on the eye surface. The acute zone is usually forward looking, but is upward looking in some insects which catch prey or mate in flight. In addition, some dragonflies have a lateral acute zone. In the acute zone the facet pattern is always more regular than elsewhere. Some acute zones, as in the locust (
Locusta
), the mantid
Orthodera
and the ghost crab
Ocypode
, are formed by reduction in Δ
ϕ
with little compensatory increase in
D
. Others such as the native bee
Amegila
, the dragonfly
Austrogomphus
, and the mantid shrimp
Odontodactylus
have larger values of
D
which match the decreasing Δ
ϕ
towards the centre of the acute zone, so that
D
Δ
ϕ
remains constant. Others again, particularly the wasp
Bembix
, the dragonflies
Hemicordulia, Orthetrum
and several mantids, show an increase in
D
which is insufficient to compensate for the large decrease in Δ
ϕ
, so that
D
Δ
ϕ
is smaller in the acute zone. A reduced
D
Δ
ϕ
in the acute zone may imply that it requires brighter light or more time than the rest of the eye in order to make full use of its increased sampling density. Mapping the regional differences of the theoretical resolving power of the ommatidia, and of the potential spatial resolution of different parts of the eye is only the first step towards understanding the functions of the different eye regions. The anatomical basis of the optics, the actual field sizes of receptors as measured physiologically, the part played by binocular overlap, the regional differences in the mechanisms of integration behind the eye, and the patterns of behaviour that are dependent on each eye region, remain to be elucidated.
Tập 285 Số 1003 - Trang 1-59 - 1978
Organic free radicals and proteins in biochemical injury: electron- or hydrogen-transfer reactions? The reactions of organic free radicals, acting as either reductants or oxidants, have been studied by pulse radiolysis in neutral aqueous solution at room temperature. Many hydroxyl-substituted aliphatic carbon-centred radicals and one-electron adducts have been shown to be good one-electron reductants, while several oxygen-, sulphurand nitrogen- (but not carbon-) centred free radicals have been shown to be good one-electron oxidants. Several carbon-centred radicals can be reduced rapidly by hydrogen transfer, from undissociated thiol compounds which can thus act as catalysts facilitating the overall reduction of a carbon-centred radical by an electron-donating molecule. Kinetic considerations influenced by the one-electron redox potentials of the radical-molecule couples involved, determine whether a particular reaction predominates. In this paper examples of such reactions, involving a water-soluble derivative of vitamin E (Trolox C) and the coenzyme NADH, are described, together with studies showing (a ) that even in complex multi-solute systems some organic peroxy radicals can inactiviate alcohol dehydrogenase under conditions where the superoxide radical does not, and (b ) the superoxide radical can be damaging if urate is also present, and this damage can be reduced by the presence of superoxide dismutase.
Tập 311 Số 1152 - Trang 545-563 - 1985
The structure of β-lactamases
The β-lactamases are widely distributed in both Gram-positive and Gram-negative bacteria. They all inactivate penicillins and cephalosporins by opening the β-lactam ring. Many varieties of the enzyme can be distinguished on the basis of their catalytic and molecular properties, but only amino acid sequence determination gives information upon which a molecular phylogeny can be based. The present evidence suggests that the β-lactamases have a polyphyletic origin. All the β-lactamases of currently known amino acid sequence belong to one homology group, here called class A enzymes. Class B consists of the mechanistically distinct
Bacillus cereus
β-lactamase II, which preliminary partial sequence analysis suggests to be structurally unrelated to the class A enzymes. It is predicted that sequence analysis will show that further classes will need to be created to account for particular β-lactamases of distinctive molecular and mechanistic properties.
Tập 289 Số 1036 - Trang 321-331 - 1980
The chemical basis of morphogenesis
It is suggested that a system of chemical substances, called morphogens, reacting together and diffusing through a tissue, is adequate to account for the main phenomena of morphogenesis. Such a system, although it may originally be quite homogeneous, may later develop a pattern or structure due to an instability of the homogeneous equilibrium, which is triggered off by random disturbances. Such reaction-diffusion systems are considered in some detail in the case of an isolated ring of cells, a mathematically convenient, though biologically unusual system. The investigation is chiefly concerned with the onset of instability. It is found that there are six essentially different forms which this may take. In the most interesting form stationary waves appear on the ring. It is suggested that this might account, for instance, for the tentacle patterns on
Hydra
and for whorled leaves. A system of reactions and diffusion on a sphere is also considered. Such a system appears to account for gastrulation. Another reaction system in two dimensions gives rise to patterns reminiscent of dappling. It is also suggested that stationary waves in two dimensions could account for the phenomena of phyllotaxis. The purpose of this paper is to discuss a possible mechanism by which the genes of a zygote may determine the anatomical structure of the resulting organism. The theory does not make any new hypotheses; it merely suggests that certain well-known physical laws are sufficient to account for many of the facts. The full understanding of the paper requires a good knowledge of mathematics, some biology, and some elementary chemistry. Since readers cannot be expected to be experts in all of these subjects, a number of elementary facts are explained, which can be found in text-books, but whose omission would make the paper difficult reading.
Tập 237 Số 641 - Trang 37-72 - 1952