摘要:

Summary1. Present‐day interest in the study of fine structure may be traced back to the work of the botanist, Carl Nägeli, to whom the conception of the micell is due.2. The continuation of Nageli's optical studies of biological structures, the development of X‐ray analysis, and the investigation of the properties of long chain high polymers, have led to the extension and modification of Nägeli's ideas.3. Two main types of molecular aggregate are of particular importance in biological systems—linear (or fibrous) and laminar structures. These may be classified as subcellular, extracellular and supracellular.4. The subcellular structures which have been examined include: protein fibres from the sap of virus‐infected plants; chromosomes; asters and spindles; and contractile fibrils (muscle fibrils, myonemes, pseudopodia and cilia). These all appear to be composed of chain molecules arranged approximately parallel to the long axis of the structure in question.Laminar subcellular structures include the surface membranes of animal cells (nerve fibres, echinoderm eggs, red blood corpuscles) and the outer portion of the rods and cones of vertebrate retinae. These are composed apparently of alternating layers of protein and lipoid molecules.5. Extracellular fibrous structures are represented by elastoidin, collagen, elastin and chitin; laminar structures by the keratinous egg cases of selachians, the cellulose test of tunicates and chitinous integuments in general. The relation of these to other natural and synthetic high polymers is discussed.6. The category of supracellular Structures, that is, of macroscopic fibrous or laminar structures of multicellular origin includes (a) hair and muscles, and (b) enamel and bone.7. It is clear that a close parallel in structure and behaviour exists between biological materials and high polymer substances. The morphological implications of this parallel are discussed and the importance of molecular morphology for the biologist is c

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1940.tb00752.x

出版商:Blackwell Publishing Ltd    

年代:1940

数据来源: WILEY

摘要:

SummaryThe effect of cyanide on the respiration of living cells makes possible the differentiation between and the description of two types of respiratory systems.(1) The cyanide‐sensitive respiration may be identified with the Warburg‐Keilin respiratory system. The normal variation in Qo1between different organs, organisms, developmental stages (in certain enumerated cases) and random variations among samples of the same tissue, seem largely to be accountable by differences in the activity of this system. The rate of oxygen consumption by this system varies over a wide range of values, and accounts for about 90% of themaximum possiblerespiratory rate of most actively aerobic tissues and organisms. It seems likely (on the basis of the available data) that the cyanide‐sensitive system tends most actively to oxidize carbohydrates and other metabolites that have a similarly high water‐solubility and O/C ratio. Thus, cyanide‐sensitive respiration is characterized by a respiratory quotient of about 1.0. The Warburg‐Keilin system also appears to be the more sensitive (of the two) to variations in temperature and po2.(2) The cyanide‐stable respiration may be identified with the yellow enzyme or flavoprotein. Its activity is relatively small and constant from organ to organ and from organism to organism (within certain groups), as compared with the activity of the cyanide‐sensitive system. It seems likely that the metabolic substrates of this respiratory system (in vivo) are restricted, in the main, to fatty compounds and other substances that have a similarly low O/C ratio. Thus, the cyanide‐stable respiration is characterized by a respiratory quotient of 0.8 or less.Hence, since most variations in the total rate of respiration are mainly due to variations in the activity of the cyanide‐sensitive system alone, percentage inhibition by cyanide (i.e. “cyanide‐sensitivity”) increases with the normal rate of respiration. Therefore, this value is no index of the relative activity of the two systems unless the substrate environment and other influential conditions are specified.Certain intrinsic properties of the Warburg‐Keilin system are elucidated bypartialinhibition of this system. It is shown thereby that the inhibitory effect of cyanide is related to the extent of saturation of the dehydrogenase with its substrate. When the dehydrogenase is only partially saturated or “covered”, the respiratory rate is reduced only by high cyanide concentrations. Thus, under such circumstances, part of the oxidase may be inactivated by a low concentration of cyanide without affecting the rate of respiration. However, such a cyanide concentration prevents the rise in respiratory rate that normally follows the restoration of the dehydrogenase to complete saturation by the addition of substrate to the medium. Thus, in this case we again note that the percentage inhibition by cyanide increases with the original (i.e. cyanide‐free) rate of respiration.It appears therefore that the respiratory systems that can be distinguished by means of cyanide‐sensitivity are to a large degree independent of each other. It has frequently been suggested that the two systems present alternative paths for the oxidation of any given metabolite. The amount of oxidative activity of each system would then depend on their relative concentrations in the cell and on their relative oxidative tendencies, i.e. redox potentials. If this were so, we would expect that the ratio of their activities would be constant regardless of the nature or concentration of the metabolite present in the medium. Furthermore, if the activity of one of these systems be curtailed (e.g. by cyanide), it follows that the insensitive system would become more active since it would then be exposed to a greater portion of the “reduction potential”) which is produced by the metabolite and its dehydrogenase.It does not seem likely, ‐therefore, that this is a valid interpretation of the interrelationships of these processes as they obtain in the living cell. The ratio of the rates of activity of the two systems (i.e. the percentage inhibition by cyanide) is not constant, but varies directly with the total rate of respiration. Thus, in a living cell the cyanide‐stable system seems to operate at a low and constant rate, to a large degree independent of the highly variable rate of activity of the cyanide‐sensitive system. Furthermore, the systems appear to have qualitative specificities as to substrates, rather than sharing the oxidation of each metabolite. These facts seem to indicate that there is no direct thermodynamic equilibrium between the oxidative activity of the two systems.The internal relationships of the various parts of the cyanide‐sensitive system appear to be equally discontinuous. Under certain conditions the saturation of the oxidase or the dehydrogenase may be altered without affecting the total rate of respiration.Finally, these specific relationships of the respiratory systems are intimately associated with the normal integrity of the cell. Destruction of the cellular protoplasm disorients the qualitative specificities that obtain in the living cell. It would appear that the ordering of the interrelated processes of cellular respiration is in some manner fa

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1940.tb00753.x

出版商:Blackwell Publishing Ltd    

年代:1940

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1940.tb00754.x

出版商:Blackwell Publishing Ltd    

年代:1940

数据来源: WILEY

摘要:

SummaryPalaeontological evidence bearing on the evolutionary origin of the Hominidae is provided by dryopithecine fossils of Miocene and Pliocene date. These fossils consist almost entirely of jaws and teeth. They indicate that, while the dentition ofDyropithecuswas essentially simian in its general characters, in certain features, notably the cusp‐pattern and proportions of the molars, it showed some significant approach to a human type of dentition. In certain allied genera, this approach is still further emphasized by the conformation of the dental arcade. The fact that in some species of these fossil apes the characteristic specializations of modem anthropoid apes were already evident in incipient form suggests that the divergence of the evolutionary line leading to the Hominidae from that which culminated in the modem genera of anthropoid apes must probably be referred to the beginning of Miocene times.More recent fossil apes from South Africa, even though they themselves may not bear any ancestral relation to man, emphasize the evolutionary potentialities of the Dryopithecinae for development in the direction of the Hominidae. However, a considerable gap still exists between the dryopithecine apes and the earliest known representatives of the Hominidae, a gap which can only be filled by further palaeon‐tological discoveries, with particular reference to the skull and limb characters of the former.The accession of new palaeontological material of thePithecanthropusgroup (including those fossils which have been referred to the genusSinanthropus) has served to emphasize its hominid status. It is important to note that, despite many primitive features of the skull, brain and dentition, the limb bones of thePithecanthropusgroup are closely comparable with those of modem man. It becomes clear that if the modem characters of the human limbs had already been acquired so early as the beginning of Pleistocene times, the point of divergence of the Hominidae from the Simiidae must have been correspondingly more remote.ThePithecanthropusgroup almost certainly provided the basis for the develop‐nent of later types of man. Of these, one is represented by the rather specialized Neanderthal type of later Mousterian date. That this is to be regarded as an aberrant line is indicated by the fact that fossil human remains of early Mousterian and pre‐Mousterian date were less distinctively “Neanderthaloid”, and more akin in their anatomical features toHomo sapiens. There seems little doubt that these fossils represent, as a group, the direct ancestors o

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1940.tb00755.x

出版商:Blackwell Publishing Ltd    

年代:1940

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1940.tb00756.x

出版商:Blackwell Publishing Ltd    

年代:1940

数据来源: WILEY

摘要:

Summary1. Oestrogens stimulate growth not only of the epithelial and fibro‐muscular tissues of the male and female urogenital tracts, but also of certain non‐reproductive tissues (e.g. skin, nasal mucosa, gums). Under normal physiological conditions oestrogenic sensitivity manifests itself histologically both in the orderly proliferation of cylindrical secretory cells (for convenience this response is referred to as “glandular”), and in the proliferation, cornification and desquamation of stratified squamous epithelium (for convenience called “squamous response”).2. In the main the glandular response is confined to tissues (e.g. uterus, hydatids of Morgagni) which are undoubtedly derived from the Mullerian duct. The squamous response, on the other hand, occurs in tissues which are stated to be derived from the Mullerian and Wolffian ducts, the urogenital sinus (entoderm) and the skin (ectoderm).3. Presumed Müllerian tissues (e.g. uterus and vagina) are thus capable of both the glandular and squamous types of response. Exmifiation of the embryo‐logical evidence on the development of the vagina in various species, and of evidence derived from the study of natural and experimental intersexuality, suggests, however, that the vaginal epithelium is ultimately derived from the urogenital sinus. It is likely that in cases where the Mullerian ducts contribute to the development of the upper part of the vagina, the Mullerian epithelium is as a rule finally replaced hy sinus epithelium.4. It is suggested that true Müllerian tissue responds to oestrogens by glandular proliferation, and that epithelial metaplasia and stratification in the reproductive tract in response to oestrogenic stimulation, whatever be its histochemical basis, may in general be regarded anatpmically as a primary response of tissue in whose development oestrogen‐sensitive sinus epithelium has either played a direct or an indirect part.5. The process of metaplasia whereby the squamous response spreads to parts of the urogenital tract in which it does not normally appear is examined. The points at which the glandular epithelium of organs opening into what was originally the urogenital sinus meets squamous epithelium derived from the sinus are unstable zones of transition, and even in normal circumstances there may be a tendency for stratified squamous epithelium to replace epithelium which is normally cylindrical (in the same way as the originally Mullerian vaginal epithelium appears to be replaced during development by cells from the urogenital sinus). This tendency is increased under the influence of oestrogenic stimulation.6. Derivatives of the oestrogen‐sensitive sinus may themselves be insensitive.7. The changes which oestrogens produce in the genital and circumgenital skin of monkeys may be regarded as the peripheral part of a total oestrogen‐sensitive epithelial zone. The most sensitive part of this zone in the female is the vagina, and to some extent, the response, under normal conditions, diminishes progressively the further one proceeds from the very sensitive central area.8. In species of monkey in which the female has a sexual skin, oestrogenic stimulation causes stratified squamous prolifkration of the male urethral epithelium. In male monkeys in which stratified proliferation of the urethral epithelium has not been observed, the corresponding females have no external sexual skin.9. Ectodermal elements appear to be involved in the development of the caudal part of the urogenital sinus.10. It is therefore concluded that although there are developmental distinctions between various urogenital tissues that respond to oestrogenic stimulation, the embryological components of the urogenital system intermix, during development, at their points of contact. Thus the caudal ends of the mesodermal Mullerian and Wolffian ducts are invaded by epithelium from the primarily entodermal urogenital sinus, and the caudal part of the sinus, in turn, is infiltrated with ectodermal cells from the cloacal region. This represents a morphogenetic reflexion of the fact that the oestrogenic responses of the circumgenital and genital skin grade, without any sharp interruption, in the female into those of the vagina, and in the male into those of the urethra, and that the responses of these two organs in turn may extend into organs

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1940.tb00757.x

出版商:Blackwell Publishing Ltd    

年代:1940

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1940.tb00758.x

出版商:Blackwell Publishing Ltd    

年代:1940

数据来源: WILEY