摘要:

SummaryWhen food is ingested by an animal in an environmental temperature above 25°C. his energy metabolism increases. This is known as the specific dynamic action of foodstuffs. The largest specific dynamic action is exerted by protein and amino acids.The specific dynamic action of injected amino acids, other things being equal, is approximately the same as protein taken by mouth. This and other evidence exclude the work of digestion and absorption as the source of this increase in metabolism. The other of the older hypotheses proposed in explanation of this phenomenon referred the increased heat production and respiration to an increased metabolism of the cells, apart from digestion, absorption and excretion. That of Voit was that the increased metabolism was a plethora effect, the result of an increased concentration of metabolites in the cell; of Rubner that the increased heat production represented reactions in which part of the protein was converted to glucose, the remainder not convertible to glucose is burned with the nitrogen‐carrying moiety. The heat produced in these reactions, according to Rubner, is not utilisable by the organism and hence appears only as heat.Lusk restated these hypotheses in terms of specific chemical reactions and subjected them to experimental test. He first took the position that though the increased metabolism following the ingestion of carbohydrate and fat were plethora effects, the calorigenic effect of amino acids was of different origin and represented a specific stimulation of the cells without the amino acids themselves necessarily undergoing oxidation. Later he modified this view and held that the specific dynamic action of amino acids represented the heat loss in converting the deaminised residues to glucose, and this specific dynamic effect was an absolute and characteristic constant for each amino acid, in spite of the fact that his observations, as a rule, terminated long before the metabolism of the amino acid administered was complete. Lusk held also that the metabolism of the nitrogen—deamination, urea formation, and excretion—was not responsible for any of the increase in metabolism observed. This contention was based mainly on the observation that glutamic acid exerts no specific dynamic effect, an observation which all other observers have shown to be erroneous. Lusk's explanation fails to account for the large specific dynamic effects of amino acids, such as tyrosine and phenylalanine, which are not converted to glucose.Although it was emphasised by Lusk (at first at any rate) that the increase in energy metabolism is proportional to the amount of protein or amino acid metabolised, the practice arose, particularly among clinical workers, of considering the increase in energy metabolism observed in the first few hours as an absolute quantity to be referred to the quantity of protein or amino acid administered, rather than to the quantity metabolised in the interval through which the energy metabolism was observed. This is chiefly responsible for the conflicting reports regarding variations in the specific dynamic action of protein in endocrine and nutritional disorders.The specific dynamic action of protein is not constant. It is usefully expressed as a ratio of calories in excess of the basal to urinary nitrogen in excess of the basal. Nearly all the data on record which can be expressed in this form are collected.A theory of the specific dynamic action of protein is presented which accounts for the variations, and the minimum and maximum values observed for the ratio of excess calories to excess urinary nitrogen. According to this theory the specific dynamic action is a composite of two factors, one nearly constant, representing the increased energy production attending the metabolism and excretion of the nitrogen, and amounts to 7–10 calories per gram of nitrogen; the other—more variable, and at times larger fraction—arises from the metabolism of the carbon.Since the amino acids do not act as primary stimulants to cellular metabolism (the evidence for this is discussed in detail) the increase in metabolism follows their deamination—hence the parallel between the increase in energy metabolism and the increased concentration of amino acids in the blood, the increased urinary excretion of uric acid in man, and of glucose in the phlorhizinised dog. For the same reason when the organs in which deamination occurs are removed—the liver, and to a lesser extent the kidneys and small intestine—injected amino acids exert no specific dynamic action; and in the normal animal the specific dynamic action is confined to the viscera.In the metabolism of the nitrogen, the heat produced in oxidative deamination is not available to the organism for work because the stoichiometrical requirements when oxygen combines directly with a metabolite must be satisfied. For the same reason in the coupled reactions whereby urea and other products (glycogen) are synthesised, the excess energy is not available for physiological work.The metabolism of the carbon is responsible for the observed variations in the specific dynamic action of protein. In general it may be compared to the recovery phase of muscular exercise. An oxygen debt is incurred, and the cost of its repayment varies with the nutritional state and the nature and fate of the deaminised residue. Accordingly the specific dynamic action of protein is not available for muscular or other work in the organism. It will vary according to the extent that the deaminised residues spare tissue carbon, whether they are converted to glucose or fat, and according to the nature of the fuel mixture supporting these syntheses and conversions.This theory accounts for most of the hitherto anomalous phenomena in the specific dynamic action of protein. Reference of the increase in metabolism to the quantity of nitrogen metabolised shows that there is no “neutralisation” of the specific dynamic effects of amino acids when these are given with protein; and the specific dynamic action of protein is not particularly low or absent in endocrine or nutritional disorders. Analysis of the physiology of coupled reactions, taking into account the mode of deamination of individual amino acids (whether oxidative or hydrolytic), and the nature of the deaminised residue indicates the reasons for the high specific dynamic effects of ketogenic amino acids such as tyrosine and phenylalanine, and of glutamic acid, and also for certain possible low figures, as in the cases of

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00500.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SummaryThe phenomena of activation and transmission in the passive iron wire model are described, and the various parallels with the irritable living system, especially nerve, are discussed. In general, the similarity of behaviour is to be referred to a single structural feature common to both systems, namely the presence of a thin, polarisable and chemically alterable interfacial layer or surface film (oxide film; plasma membrane) situated at the boundary between the metal, or the protoplasm, and the surrounding medium. This film undergoes characteristic changes of chemical composition and physical properties,e.g.of permeability and electrical polarisation, when traversed by an electric current of an intensity and duration sufficient to produce a certain critical degree of chemical decomposition. The activity of the system as a whole is controlled by the electrochemical oxidations and reductions occurring in the film under these conditions. Hence both the model and the living system are electrically sensitive and transmit local states of activity, local changes on the film being associated with local electric circuits which have electrochemical effect at regions beyond. Hence, also, the essential conditions under which electrical activation occurs are the same in both systems (polar activation, intensity‐duration relationship, etc.). Activation and transmission are similarly affected in both by changes of temperature, by variations in the composition of the medium, by electrical polarisation (analogy to electrotonus), and by surface‐active compounds (analogy to narcosis). Closely analogous processes of progressive recovery occur in both systems after the passage of an activation wave (refractory phase). Other resemblances are seen in the phenomena of automatic rhythm, the mutual interference of activation waves, the transmission of inhibitory influence, irreciprocal transmission, and distance influence, excitatory and inhibitory. Biological analogies of a more general kind, relating to mutual interdependence between processes occurring in spatially separated regions traversed by the same electric current—a possible factor in certain types of integration—are briefly di

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00501.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

ZusammenfassungI. Reaktionen auf Schallreize wurden bisher an 32 Fischarten (aus 14 Familien) zuverlässig nachgewiesen.2. Spontane Reaktionen auf Töne sind nicht zu erwarten, da die von uns angewendeten Tonsignale für die Fische keine biologische Bedeutung haben. Zuverlässige Reaktionen erhält man daher nur nachDressurauf Töne. Diese Methode ermöglicht auch eine weitgehende Analyse des Hörvermögens bei Fischen.3. Die obere und untereHörgrenzeist bei Fischen mit gut entwickeltem Gehörsinn angenähert dieselbe wie beim Menschen.4. Die Fähigkeit derTonunterscheidungist für Elritzen (Phoxinus laevis) und Zwergwelse (Amiurus nebulosus) sicher nachgewiesen. Bei einem Intervall von etwa einer Oktave wurden zwei verschieden hohe Töne im Gedächtnis behalten und wiedererkannt. Der beste Fisch lernte sogar die Unterscheidung einer kleinen Terz. Auch mehr als zwei (bis zu fünf) Töne können gleichzeitig im Gedächtnis behalten werden.5. DieHörschärfeist bei den geprüften Cypriniden, Siluriden und Characiniden angenähert dieselbe wie die des menschlichen Ohres.6. Bei der Elritze (Phoxinus laevis) ist die pars inferior des Labyrinths, also Sacculus und Lagena, der Sitz des Gehörsinnes. Die pars inferior hat keine statische Funktion. Die pars superior (Utriculus und Bogengänge) ist der Sitz des Gleichgewichtssinnes; dieser Teil des Labyrinths hat keine Hörfunktion.7. Tiefe Töne (unter 100–150 v.d.) werden, wenn sie sehr intensiv sind, von der Elritzeauchdurch den Tastsinn der Haut, sehr tiefe Töne (16 v.d.)nurdurch den Tastsinn wahrgenommen.8. Bei denOstariophysen(Cypriniden, Siluriden, Characiniden und Gymnotiden) steht die Schwimmblase durch die Weberschen Knöchelchen mit dem Sacculus in Verbindung. Der Sacculus‐Otolith ist zum Auffangen der auf diesem Wege zugeleiteten Schallwellen besonders umgestaltet. Hierdurch erklärt sich die abweichende Form der pars inferior bei den Ostariophysen. Diese Einrichtung dient derSteigerung der Hörschärfe.9. DieNicht‐Ostariophysensind daher im allgemeinen für Schallreize weniger empfindlich. Dass auch sie durch die pars inferior des Labyrinths hören, ist noch nicht überzeugend nachgewiesen, aber ausserordentlich wahrscheinlich.10. Auch bei manchen Nicht‐Ostariophysen finden sich Einrichtungen, die der Steigerung der Hörschärfe dienen dürften. Sie sind aber physiologisch noch nicht untersucht.11. Das Labyrinth der Fische vermittelt eine Tonwahrnehmung und Tonunterscheidungohne Basilarmembran.Die Basilarmembran im Ohr der Landwirbeltiere ist wahrscheinlich ein Apparatzur Verfeinerung des Tonunterscheidungsvermögens.12. Die Fähigkeit derTonerzeugungdürfte bei Fischen sehr weit verbreitet sein. Daher ist auch die biologische Bedeutung ihres Hörvermogens nicht so rätselhaft, wie sie früher erschien.Summary1. Reactions to sound stimuli have so far been reliably demonstrated in 32 species of fishes (14 families).2. Spontaneous reactions to musical tones are not to be expected, since the sound signals used by us have no biological significance for fishes. Reliable reactions can therefore only be obtained by conditioning to tones. This method also allows of a thorough analysis of the capacity of hearing in fishes.3. The upper and lower limit of hearing in fishes that have a well‐developed capacity of hearing is approximately the same as in man.4. The capacity of discrimination of frequencies has been shown certainly to exist in minnows (Phoxinus laevis) and in a cat‐fish (Amiurus nebulosus). Two different frequencies about an octave apart could be remembered and recognised. The best fish learned even to discriminate a minor third. And more than two (up to five) tones can be remembered at the same time.5. In the Cyprinidae, Siluridae and Characinidae tested, the sensitiveness of hearing is approximately the same as that of the human ear.6. In the minnow (Phoxinus laevis) the pars inferior, that is the sacculus and the lagena, is the seat of the sense of hearing. The pars inferior has no static function. The pars superior (utriculus and semicircular canals) is the seat of the sense of equilibrium; this part of the labyrinth has no auditory function.7. In the case of the minnow, low frequencies (below 100–150) are perceived also by the touch sensitivity of the skin if they are of high intensity, while very low frequencies (16) are perceived by the touch sense only.8. In Ostariophysi (Cyprinidae, Siluridae, Characinidae and Gymnotidae) the swim bladder is linked up with the sacculus by the Weberian ossicles. The saccular otolith is specially modified for the reception of the sound waves directed towards it by the above mechanism. That explains the special shape of the pars inferior in the Ostariophysi. These dispositions are responsible for the increase iii sensitiveness of hearing.9. Fishes other than the Ostariophysi are therefore generally less sensitive to sound stimuli. It has not yet been convincingly proved that these fishes also hear by means of the pars inferior of the labyrinth, but this is very probably the case.10. In some of the non‐Ostariophysi there are, nevertheless, structures which may serve in increasing the sensitiveness of hearing. These have hot vet been investigated physiologically.11. The labyrinth of fishes has the capacity of the reception of sound and the discrimination of tones, though it has no membrana basilaris. The membrana basilaris in the ear of land vertebrates is probably an organ for the refinement of tone discrimination.12. The capacity of sound production appears to be very common in fishes. The biological significance of their ability to

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00502.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SummaryI. Arginase is a highly specific intracellular enzyme and requires that both the carboxyl and the guanidine groups shall be free if the substrate molecule is to be activated. The kinetics of arginase and its behaviour towards activators and inhibitors are very briefly discussed in the text.2. Arginase is abundantly present in the liver of ureotelic vertebrates; small amounts are present also in the kidney and testis, but little or none elsewhere. In uricotelic vertebrates it is mainly confined to the kidney.3. Male animals always contain about 50 per cent, more arginase than females; a sudden increase in the arginase content of the testis at puberty suggests a possible specific relation between sex and the distribution of arginase.4. Arginase is widely distributed among invertebrates, usually in small amounts. But the terrestrial gastropods contain as much of the enzyme as do the ureotelic vertebrates.5. The synthesis of urea by ureotelic vertebrates takes place by a cyclical mechanism involving arginase. This system is present in mammals, chelonian reptiles and Amphibia, but not in birds. It is very probably present in the elasmobranch fishes also, and the possibility that it is present in the teleosts remains open.6. Although arginase is not concerned in the production of uric acid by uricotelic vertebrates it does account for such urea as is excreted by these forms. Its main function in the birds is that of supplying ornithine for detoxication.7. Many invertebrates resemble the birds in possessing small amounts of arginase, which probably suffice to account for the urea which they excrete. In the terrestrial gastropods it is possible that metabolism is primarily ureotelic as in the mammals, but that urea is secondarily converted into uric acid as an adaptation to xerophilous life.8. Although many bacteria are capable of breaking down arginine they probably contain no arginase but only guanidinodesimidase. This enzyme appears to be absent from vertebrate tissues.9. Arginase is present early in embryonic life and is soon capable of discharging its adult function. But there exists a correlation between a high growth rate and a high content of arginase, phosphatase and nuclease, which suggests a specific association between arginase and the processes of growth.

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00503.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SummaryDisease relationships in grafted plants and chimaeras are shown to have both theoretical and practical significance.Grafting experiments have been employed as a means of investigating the nature of resistance and susceptibility to diseases caused by pathogenic fungi and bacteria. The effects of grafting may be direct, owing to transmission through the graft union of the substance or substances actually responsible for the reaction concerned, or indirect, due to a change in the normal response to environmental conditions. Negative results, while necessarily inconclusive, indicate that resistance and susceptibility are either genotypic properties of the protoplasm, or else are due to some factor that is not, as such, transmissible.Inoculation experiments have also been used in the interpretation of graft hybrids and chimaeras. In the case of the artificially inducedSolanumchimaeras, experiments withSeptoria lycopersicihave shown that the two components retain their characteristic reaction to infection unaltered. Unless this assumption can be made in other forms, whose mode of origin is unknown, it becomes impossible to distinguish the two components, as such, from the modified tissues of a true graft hybrid. Results with the Crataegomespili and Pirocydoniae are not altogether consistent with the periclinal chimaera theory.Examples are given of the practical importance of grafting in the prevention and control of disease and mechanical injury in fruit trees and other ornamental trees and shrubs. Choice of suitable stocks may entirely prevent leaf scorch and other physiological disorders, and a large body of information has accumulated concerning the influence of root‐stock on quality and storage life of the fruit.The importance of incompatibility between stock and scion is discussed, and examples are quoted in which grafting has led to the transmission of an unsuspected virus disease. Improper fitting and tying of the graft union is liable to result in the production of wound overgrowths, and also increases the danger of external infectio

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1936.tb00504.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY