Showing papers in "Biological Reviews in 1937"

Über drüsen-nervenzellen und neurosekretorische organe bei wirbellosen und wirbeltieren

Abstract: Zusammenfassung Wir stellen hier die “Drusen-Nervenzelle” als einen neuen Zelltypus zur Diskussion. Wir verstehen darunter Nervenzellen, die mehr oder weniger das Bild sekretorisch tatiger Elemente bieten und die innerhalb des Zentralnervensystems in der Regel wohl abgrenzbare “Organe” bilden, wie z. B. die Zwischenhirndruse der Wirbeltiere. Im einzelnen kann auf Grund des bis jetzt vorliegenden Materials bezuglich dieser Zellen folgendes festgestellt werden: 1Die Drusen-Nervenzellen sind weit verbreitet. Unter den Wirbellosen wurden sie bei Anneliden, Mollusken, Crustaceen und Insekten gefunden. In ihrem feineren Aufbau konnte eine vollkommene Ubereinstimmung zwischen den Drusen-Nervenzellen bei den Bienen und bei den Opisthobranchiern festgestellt werden. Bei den Wirbeltieren finden sich lebhaft sekretorisch tatige Zellen in erster Linie im Zwischenhirn und zwar bei Selachiern, Knochenfischen, Amphibien, Reptilien, Saugern und beim Menschen. Bei Knochenfischen wurden Drusen-Nervenzellen weiterhin im Kern des Nervus terminalis, im Haubengebiet des Mittelhirns und bei einzelnen Arten im Schwanzabschnitt des Ruckenmarks festgestellt. Bei Selachiern (Raja) sind diese letzteren besonders gut entwickelt. Die Drusen-Nervenzellen kommen also bei Wirbellosen und Wirbeltieren in verschiedenen Abschnitten des zentralen Nervensystems vor. 2Es handelt sich um echte Nervenzellen oder um von Nervenzellen abzuleitende Elemente. Die grossen Drusenzellen im terminalen Ruckenmarksabschnitt der Rochen entwickeln sich aus den gleichen Neuroblasten wie die Vorderhornzellen des Ruckenmarks. Bei Knochenfischen konnen ferner bei vergleichender Untersuchung einer grosseren Anzahl von Arten alle Ubergange beobachtet werden von typischen Nervenzellen ohne histologisch nachweisbare Sekretproduktion (z. B. Salmo fario) uber verschiedene Grade der Kolloidbildung und -speicherung (Tinea vulgaris, Phoxinus laevis, Fundulus heteroclitus) bis zur Umwandlung der Zellen in Drusenzellen, die alle nervosen Charaktere vermissen lassen (Cristiceps argentatus, Galeichthys feliceps). Auch bei den Amphibien steht die nervose Natur der Zellen ausser Frage, denn auch solche Zellen, die mit Sekretgranula aller Grossen angefullt sind, lassen doch deutlich lange Auslaufer und Nisslschollen erkennen. 3Gemeinsam ist allen Drusen-Nervenzellen der Wirbellosen und Wirbeltiere die Bildung und Abgabe von Granula und Kolloidtropfen. Diese treten teils im Plasma selbst auf (Aplysia, Pleurobranchaea, Bufo), teils sind sie in Vakuolen eingeschlossen (Raja, Cristiceps). Ihre Farbbarkeit ist unspezifisch. 4Fur die Mehrzahl der bisher beobachteten Drusen-Nervenzellen ist ein ausgepragter Kernpolymorphismus charakteristisch. So sind die Kerne der Drusen-Nervenzellen im Ruckenmark von Raja, im Nucleus lateralis tuberis von Esox lucius und Tetrodon lagocephalus, in der Mittelhirndruse von Phoxinus laevis u.s.w. vielfaltig gelappt und verzweigt, sodass auf dem Schnitt Bilder wie von polymorphkernigen Leukocyten oder vielkernigen Riesenzellen entstehen. Der lebhafte Stoffwechsel der sekretorisch tatigen Nervenzellen macht wohl eine grosse Kernoberflache notwendig, die hier, wie auch sonst vielfach bei Drusenzellen, durch eine gelappte und verzweigte Form des Zellkerns erreicht wird. 5Ebenfalls im Zusammenhang mit dem lebhaften Stoffaustausch der Drusen-Nervenzellen steht ihr Verhalten zu den Gefassen. So ziehen jeweils vier bis funf Kapillaren um eine der grossen Drusen-Nervenzellen im Ruckenmark von Raja; bisweilen ist eine Kapillare auch ganz vom Zelleib eingeschlossen. Solche perizellulare und endozellulare Kapillaren wurden auch in den sekretorisch tatigen Zwischenhirnkernen der Wirbeltiere beobachtet. 6Welche Stoffe in den durch histologische Untersuchung bis jetzt bekannt gewordenen intrazentralen Drusengebieten gebildet werden und welche physiologische Bedeutung ihnen zukommt, ist noch unerforscht. Summary In this article the gland-nerve cell is considered as a new type of cell. By the term “gland-nerve cell” is meant nerve cells having more or less the appearance of secretory cells. They may form well-delimited “organs” within the central nervous system, as, for example, the diencephalic gland of vertebrates. The following facts are known concerning these cells. 1Gland-nerve cells have a wide distribution. Among the invertebrates, they have been found in annelids, molluscs, crustaceans and insects. There is a close resemblance in detailed structure between the gland-nerve cells of bees and of opisthobranchs. In the vertebrates, active secretory cells are found chiefly in the diencephalon of selachians, teleosts, amphibia, reptiles, and mammals, including man. In the bony fishes, gland-nerve cells have also been found in the nucleus of the nervus terminalis, in the midbrain, and, in some genera, in the caudal region of the spinal cord. In selachians (Raia) they are specially well developed. Thus gland-nerve cells occur in various regions of the central nervous system both of invertebrates and vertebrates. 2Gland-nerve cells are either true nerve cells or are derivatives of nerve cells. The large gland cells in the terminal region of the spinal cord of the skate develop from the same neuroblasts as the cells in the anterior horn. In bony fishes, all stages can be found from typical nerve cells without histologically visible secretory products (Salmo), through cells with varying degrees of colloid formation and storage (Tinca, Phoxinus, Fundulus), to cells transformed into gland cells lacking any nervous character (Cristiceps, Galeichthys). The nervous nature of such cells cannot be doubted in the amphibia, for even cells which are filled with secretory granules of all sizes have long processes and Nissl granules. 3All gland-nerve cells, both of invertebrates and vertebrates, produce granules and drops of colloid. In some cases these secretions appear in the cytoplasm itself (Aplysia, Pleurobranchaea, Bufo), in other cases they are included in vacuoles (Raia, Cristiceps). Their staining properties are non-specific. 4A marked nuclear polymorphism is characteristic of most gland-nerve cells. Thus the nuclei of such cells in the spinal cord of Raia, in the nucleus lateralis tuberis of Esox and Tetrodon, in the midbrain gland of Phoxinus, etc., are lobed and branched, so that the aspect of polymorphonuclear leucocytes or multinucleate giant cells is given in sections. Doubtless the active metabolism of secretory nerve cells requires a large nuclear surface, supplied here, as is often the case in gland cells, by the lobed and branched form of the nucleus. 5The relation of gland-nerve cells to blood vessels is likewise connected with their active metabolism. Thus four or five capillaries sometimes surround a large gland-nerve cell in the spinal cord of Raia, and a capillary may be enclosed by the cell body. Such pericellular and endocellular capillaries have also been observed in the secretory diencephalon nuclei of vertebrates. 6It is as yet unknown what substances are secreted by glandular regions of the central nervous system and what is their physiological role.

The beginning of the age of mammals

Abstract: The mammals of the Paleocene, first epoch of the Tertiary, the Age of Mammals, are essential for the elucidation of numerous zoological, biological, and geological problems. Among these problems are determination of the affinities of mammals in general, of their ancestral and primitive structures and of the course of their evolution, as well as problems of the origin and nature of adaptations and habits, and more special and, in one sense, practical problems of stratigraphy and some other branches of geology. The first known Paleocene mammal was described in 1841, but intensive work began with Lemoine's first publication in 1878. Since that time work has continued at ever accelerated pace, by Cope, Osborn, Wortman, Matthew, Granger, Sinclair, Douglass, Gidley, Schlosser, Teilhard, Jepsen, Russell, Patterson, Simpson, and others. A nearly complete sequence of Paleocene mammalian faunas is now known from North America, and more limited but also important faunas are known from Europe, Asia, and South America. These faunas include multituberculates, marsupials and placental mammals, classified in seventeen orders, the general characters of which in the Paleocene are eviewed. From these mammals it is possible to infer with high probability the ancestral characters of placental mammals in general, the evidence for a primitive “tritubercular” or trigonal-tuberculosectorial primitive molar type being particularly conclusive and important. The Cretaceous-Paleocene transition in North America is marked by the disappearance of dinosaurs and the appearance of several orders of mammals apparently as immigrants from some unknown region. The Paleocene sequence on the same continent, which still has two breaks not represented by known faunas, is marked not only by great evolutionary advance but also by progressive enriching of the faunas, chiefly by the appearance of new and generally more progressive mammalian groups as immigrants. The Paleocene-Eocene line is drawn at the culmination of this faunal change. Although in detail the change is by intergradation and gradual transition, from a broader point of view it marks a very radical difference in mammalian faunal type, the Paleocene forms eventually disappearing and the Eocene forms being the forerunners of the later Tertiary and Recent faunas. The same faunal change eventually occurred in South America, but at a much later date, around the end of the Tertiary. In the Upper Paleocene Asia, Europe, North America, and South America all show considerable local differentiation but give evidence of the derivation of their faunas from a common source. Those of North America and Europe are fairly similar, although not identical, and that of South America is most distinctive, evidence of longer separation from the other continents. In a general summary of known mammalian faunal history the few known Triassic mammals have no clear significance. The Jurassic mammals of Europe and North America are of distinctive type, with four primitive orders. From two of these developed the multituberculates, marsupials and insectivores of the Upper Cretaceous. Further differentiation of these three, but particularly of the general placental, carnivore-insectivore stock produced the typical Paleocene faunal type. Finally, progressive evolution and diversification of the several Paleocene placental mammal stocks gave rise to the Eocene faunal type which still exists to-day. Summary of Mammalian Faunal History The oldest known mammals, from the Rhaeto-Lias in Europe and Africa, do not include the ancestors of the later mammals and have little bearing on mammalian faunal succession (see Simpson, 1928b). The Middle Jurassic fauna of England and the Upper Jurassic faunas of England, the United States, and East Africa (one specimen) are of a distinctive faunal type and suggest that this sort of mammalian fauna had then spread over a large part of the world. They include multituberculates, triconodonts, symmetrodonts, and pantotheres (Simpson, 1928c, 1929c). The multituberculates reappear, in more advanced and varied form, in the Cretaceous and Lower Tertiary. The triconodonts and symmetrodonts do not reappear and probably became extinct during the early Cretaceous. The known pantotheres seem to represent a Jurassic radiation from the common marsupial-placental stock. The known Upper Cretaceous faunas also are of a distinctive faunal type, but one quite different from that of the Jurassic. They consist of multituberculates (Asia and North America), marsupials (North America), and very primitive placentals of rather undifferentiated insectivore-carnivore type, classified as Insectivora (Asia and North America) (Gregory & Simpson, 1926; Simpson, 1928d). The latter apparently represent primary dichotomous differentiation of the general pantothere stock, with a secondary local radiation within each group. The known Paleocene faunas of North America, Europe, Asia, and South America probably all had a common source and represent the radiation of a fauna derived from one of the known Cretaceous types but much more highly differentiated. Among the multituberculates and marsupials this differentiation was of relatively minor grade, in taxonomic terms of family or at most subordinal rank, while the more progressive and adaptive placentals show the beginnings of a more profound splitting, ultimately of ordinal rank,1 and are more numerous and varied. In North America, at least, this new faunal type appears as an invasion from some unknown evolutionary center. In Europe, North America, and Asia, a new type of fauna began to appear during the Paleocene, the change culminating at the end of the epoch and becoming entirely complete during the Eocene. The new fauna is less markedly different from the old than in the previous changes noted, and consists of the appearance of new or “modernized” groups clearly derived from an already partly differentiated fauna of Paleocene type. The new forms appear to be immigrants where found, and came from some unidentified area where the earliest Paleocene fauna was well developed and where its rapid and diversified evolution was permitted and stimulated. Only placental mammals were involved, the few surviving multituberculates and marsupials clearly being stragglers from the known Paleocene. There has not been any other major spread of mammals or great change in faunal type. With positive changes resulting from long evolution and from repeated intermigration and negative changes resulting from extinction, the mammals now peopling at least the Holarctic continents are essentially those that appeared there in the Eocene invasion. In South America this change was long delayed, and what is essentially the incursion of the Holarctic Eocene fauna into the previous habitat of the Paleocene fauna took place at the end of the Tertiary and not toward its beginning as in Holarctica. In Australia this change never took place (aside from the agency of man). The early faunal history of Africa is unknown and still beyond logical conjecture.

Evolution and adaptation in the digestive system of the metazoa

Abstract: Summary 1Digestion in the primitive animals must have been intracellular, as it remains in the Protozoa and in the Porifera. It has persisted, to a greater or less extent, in a number of Metazoa. These may be divided into two groups: (1) those which are primitive in structure, e.g. Coelenterata, Ctenophora, most Turbellaria, and Limulus; and (2) those which are more highly evolved but have retained intracellular digestion in correlation with their mode of feeding, e.g. Brachiopoda, Rotifera, Tardigrada, Pyncogonida, Arachnida (other than Limulus) and the majority of Mollusca excluding the Cephalopoda. These animals either feed on finely divided food (collected by ciliary mechanisms or scraped by a radula) or on fluid or semi-fluid food which is sucked in. 2In certain cases, notably the Lamellibranchia, but also in the Echinodermata, intracellular digestion is assisted or exclusively carried out by wandering phagocytic blood cells. 3Extracellular digestion, originally developed with the increased size of available food as an aid to intracellular digestion, has completely replaced the more primitive form of digestion in certain rhabdocoel Turbellaria (probably), Polyzoa, Annelida, Myriapoda, Crustacea, Insecta, Cephalopoda and Chordata. This mode of digestion results in the reduction of the ingestive region of the gut and enables digestion, and the removal of indigestible material, to be hastened. The resultant increase in the rate of metabolism has had profound effects on the evolution of the Metazoa. 4The appearance of extracellular digestion has been accompanied by changes in the structure and physiology of the gut. Distinct regions have been specialized for (1) the reception of food, (2) its conduction and storage, (3) digestion and internal triturition, (4) absorption, and (5) conduction and formation of faeces. 5There is a definite correlation between the food of any animal and the nature and relative strengths of its digestive enzymes. Certain animals have acquired specific enzymes which enable them to exploit additional sources of food, the most important of such enzymes being cellulase and chitinase. 6There is a periodicity of secretion in the digestive glands of many Metazoa, e.g. Gastropoda and Crustacea. In the Lamellibranchia and in style-bearing Gastropoda, the style constitutes an ideal mechanism for the continuous liberation of small quantities of enzyme (amylase). 7The pH of the gut is controlled in various ways in different phyla. In ciliary-feeding animals this may be of importance not only in securing the optimum conditions for the action of extracellular enzymes but also by its influence on the viscosity of the mucus with which the food is entangled. 8There is evidence that the time taken for passage of food through the gut at any normal temperature corresponds to the period which is optimal for enzymatic action at that particular temperature. 9The most successful groups of animals are (1) those which possess feeding and digestive mechanisms capable of utilizing, as a result of morphological and physiological adaptations, many types of food, e.g. Annelida, Crustacea, Insecta, Gastropoda and Vertebrata, and (2) those in which one type of food is collected and digested with great efficiency, e.g. Coelenterata, Turbellaria, Arachnida, and Cephalopoda (carnivorous); Brachiopoda, Lamellibranchia, and Tunicata (ciliary feeders); Trematoda and Cestoda (parasites). Of these, the first have been by far the more successful, owing to their capacity for exploiting new sources of food, in the invasion of new habitats.

The interpretation of the flower: a study of some aspects of morphological thought

Abstract: Summary In the introduction to this study, the chief phases in the interpretation of the flower, from Goethe's day onwards, are briefly indicated in their historical sequence. Goethe's theory of the equivalence of the vegetative shoot to the flower, in the angiosperms, is then discussed and an attempt is made to evaluate the evidence for it. It is shown that this theory, if understood in a broad sense, harmonizes with the modern holistic trend in morphology. It is suggested that the flower is comparable with a vegetative shoot in a condition of permanent infantilism. Special emphasis is laid upon the inflorescence as offering, in some respects, an intermediate term between the vegetative shoot and the flower. After a brief consideration of bracts, sepals, petals and stamens, the Candollean theory of the carpel is discussed, and it is concluded that it has been peculiarly successful in providing a framework for the vast plexus of facts which it is its task to correlate. Some of the difficulties which have been felt in regard to this theory are considered, with special reference to recent work on the gynaeceum structure of the Papaveroideae. The stigma and “transmitting tissue” are then discussed, and it is concluded that there is nothing in the behaviour of this tissue which is out of harmony with the Candollean theory of the carpel. An attempt is made to arrive at a more precise notion of the meaning to be attached to correspondence, equivalence and homology, when these terms are used in connexion with Goethe's comparison of the vegetative and reproductive parts. It is suggested that these terms are best translated into the language of modern thought by the word parallelism, thus avoiding the use of Goethe's type concept, which cannot be safely employed unless its abstractness is constantly borne in mind. The nineteenth-century phase, in which morphological ideas were lifted bodily into an historical setting, is then discussed, and emphasis is laid upon the danger of thus confusing two irreducible worlds of thought. Certain attempts which have been made to relate the flower of the angiosperm to the reproductive organs of plants of earlier geological periods are briefly criticized. In the concluding sections, attention is drawn to the current reaction against phylogenetic morphology, and in favour of the purely comparative morphology contemplated by Goethe. A slight sketch is given of Delpino and Troll's theories of the flower, in which “form” is considered as distinct from “organization”. Whether these views are accepted or not, the “Gestaltlehre” is at least an indication that the morphological ideas, which Goethe initiated before the end of the eighteenth century, may even to-day suggest fresh approaches to the problem of the interpretation of the flower.

Population problems of social insects

Abstract: CONTENTS PAGE . . . . . . . . . . . . . I . Termites . 394 ( I ) General biology of termite colonies . . . . . . . . . 394 (2) Quantitative data on termite populations . . . . . . . . 394 (3) Potential immortality and foundation of the colony . . . . . . 395 (4) Description of Kulotermes colonies . . . . . . . . . 396 ' 398 ( 5 ) Conclusions . . . . . . . . . . . . I1 . Ants . . . . . . . . . . . . . . . ( I ) General biology of ant colonies and their foundation . . . . . . (2) Quantitative data on ant populations . . . . . . . . . (3) The early history of ant colonies . . . . . . . . . (4) Fertility and longevity of ants . . . . . . . . . . ( 5 ) Conclusions . . . . . . . . . . . . . I11 . Social wasps . . . . . . . . . . . . . . ( I ) General biology of wasp colonies . . . . . . . . . (2) Quantitative data on wasp nests . . . . . . . . . (3) Dynamic analysis of the seasonal population trend in a nest of Vespa crabro . . (4) The number of cells in relation to the total annual production of the wasp colony ( 5 ) Conclusions . . . . . . . . . . . . . IV . Humble-bees . . . . . . . . . . . . . . 399 399 400 401

The specificity and collaboration of digestive enzymes in metazoa

Abstract: Summary 1 The identity of the digestive enzymes found in vertebrates and invertebrates has been discussed. For the proteases the conclusion is reached that in the vertebrates as well as in the invertebrates (as far as investigated) the protein molecule is attacked by at least four different enzymes, a proteinase, carboxypolypeptidase, aminopolypeptidase and dipeptidase, which can be separated by adsorption. (Recent researches have, moreover, demonstrated the presence of a separate protaminase in the former trypsin of vertebrates.) The proteinase of Maia squinado has the same specificity and properties as the vertebrate trypsin. In the midgut gland of Helix a cathepsin is present. Further investigations must verify the distribution of these enzymes for other groups. In the vertebrates the action of these enzymes is preceded by that of pepsin (stomach), working in a strongly acid medium. This pepsin is nowhere found in invertebrates. The nature and distribution of the proteases seems to be the same for all the classes of vertebrates. It is doubtful whether the enterokinases of the vertebrates are entirely identical. The amylases of vertebrates are, as far as is known, α-amylases. They need activation by salts (chiefly sodium chloride). The amylases of invertebrates resemble those of vertebrates. An inulase is not found in vertebrates, but is present in some invertebrates. Cellulase and hemicellulase (it is doubtful whether they are identical or not) are also lacking in the vertebrates, but are present in some invertebrates. The properties of these enzymes have been fully treated. The disaccharases of vertebrates are saccharase, maltase and lactase. Of these, maltase is the most common in the invertebrates, occurring together with amylase (though its separation has not yet been carried out). Some invertebrates, especially Helix pomatia, are able to hydrolyse many more sugars (also tri- and tetrasaccharides) than the vertebrates can do. These disaccharases are still awaiting further investigation. The fat- and ester-splitting digestive enzymes of invertebrates have more the character of esterases than of lipases (or an intermediate character), whereas in the vertebrates the reverse is the case. 2 The differences in localization of the vertebrate and invertebrate digestive enzymes have been discussed. It has been pointed out that in the vertebrates the digestive enzymes occur in chains and attack the food successively, whereas in invertebrates almost all the enzymes meet in the place where the digestion is performed and attack the food simultaneously. Through this localization the action of the pepsin of the vertebrates becomes possible, for which a medium with strongly acid reaction is required, and moreover the organism is protected against inundation with cleavage products. Only in fishes (and probably amphibia) among the vertebrates is no pronounced chain of carbohydrases present, but amylase and maltase are chiefly found together in the pancreas.

Über die sekretion und resorption von gasen in der fischschwimmblase

Abstract: Zusammenfassung 1 Nach Besprechung der Zusammensetzung der Schwimmblasengase bei verschiedenen Fischarten werden die physikalischen Verhaltnisse erortert, unter denen sich einmal die im Wasser gelosten Gase und ferner die Schwimmblasengase befinden. Auf Grund dieser Tatsachen muss eine entgegen dem Diffusionsgefalle stattfindende Ausscheidung von Gasen, und zwar von Sauerstoff und von Stickstoff in der Schwimmblase, jedenfalls bei den meisten Fischen, angenommen werden. 2 Eine derartige Gasausscheidung erfolgt immer bei einer Erhohung des spezifischen Gewichtes, eine Resorption von Gasen bei Veringerung des spezifischen Gewichtes des Fisches; dabei sind in der Hauptsache Anderungen des Sauerstoffgehaltes der Blasengase zu beobachten. 3 Die Gasausscheidung steht unter Nerveneinfluss, und zwar verlaufen im Vagus die die Gasausscheidung fordernden Impulse, im Sympathicus die sie hemmenden Impulse. Die Einstellung des spezifischen Gewichtes, durch Gasausscheidung oder Gasresorption, erfolgt reflektorisch, wobei als auslosender Reiz eine Bewegung oder Abbiegung von Flossen funktioniert. 4 Physostomen, und anch Jungfische einiger Physoklisten, die eine Zeit lang einen offenen Luftgang besitzen, konnen durch Verschlucken atmospharischer Luft an der Wasseroberflache die Schwimmblase mit Gas fullen. Daneben findet aber bei vielen Physostomen eine, nur meist viel tragere Gasausscheidung wie bei den Physoklisten statt. 5 Als Ausscheidungsort fur die Blasengase kommt die sogenannte Gasdruse in Betracht, auf deren histologischen Aufbau und Blutversorgung (Wundernetze) genauer eingegangen wird. Versuchsergebnisse sprechen dafur, dass hier eine dauernde Gasausscheidung stattfindet, zu der im Bedarfsfalle eine zusatzliche, nervos regulierte Tatigkeit der Gasdruse hinzukommt. 6 Die Gasresorption erfolgt in dem “hinteren Gefassorgan” (Oval), wobei hauptsachlich Diffusionsvorgange eme Rolle spielen. Aber auch andere Teile der Blasenwandung sind fur Gase, ganz besonders auch fur Kohlensaure durchlassig. 7 Zum Schluss werden die verscniedenen Theorien, die zur Erklarung des Vorganges der Gassekretion aufgestellt worden sind, kritisch besprochen. Wahrend von einigen Forschern angenommen wird, dass tatsachlich in den Gasdrusenzellen, entsprechend ihrer Lage als ein die Blase auskleidendes Epithel die Gassekretion stattfindet, wird besonders neuerdings der Gasdruse nur die Fahigkeit der Bildung eines besonderen Sekretes zugeschrieben, das in die Blutkapillaren abgeschieden wird und in diesen, hauptsachlich in den Wundernetzen, eine Erhohung der Gasspannung hervorrufen soil. Dies Sekret soil sauren Charakter besitzen, die Kohlensaurespannung des Blutes erhohen, die wiederum zu einer Erhohung der Sauerstoffspannung des Blutes fuhrt. In den Wundernetzen soil durch Diffusion und mehrmalige Wiederholung dieses Vorganges eine Erhohung der Sauerstoffspannung im Blute stattfinden, bis schliesslich durch Diffusion Sauerstoff in die Schwimmblase gelangt. Es werden Bedenken und Versuchsergebnisse angefuhrt, die gegen das alleinige Vorhandensein dieses zuletzt beschriebenen Mechanismus sprechen, und die es wahrscheinlich machen, dass dieser Vorgang der Zunahme des Sauerstoffdruckes durch Erhohung des Kohlensaurepartialdruckes nur eine vorbereitende Aufgabe besitzt, um den Gasdrusenzellen die Bildung ihres Sekretes zu erleichtern, bei dessen Zerfall Sauerstoff und Stickstoff in der Schwimmblase gegen jeden Druck frei werden. Summary 1 The composition of the gases in the swim-bladders of different fishes is first considered, after which the physical conditions are discussed under which gases are found when dissolved in water and when present in swim-bladders. It follows from the data that there must be a liberation of gases, particularly of oxygen and nitrogen, into the swim-bladder against the diffusion gradient. 2 Gas liberation always occurs when the specific weight of the fish rises, while gas is resorbed when the specific weight falls. On these occasions it is especially the oxygen content of the bladder which is altered. 3 Gas liberation is under nervous control. The nerve impulses causing an increase in gas liberation pass through the vagus and the inhibitory impulses pass through the sympathetic. The establishment of the specific weight, whether through gas liberation or resorption is a reflex, of which the stimulus is a movement or flexion of fins. 4 Physostomids, and also the young of some physoclystids which have an open pneumatic duct for a certain time, can fill the swim-bladder with gas by swallowing air at the water surface. But, in addition to this, many physostomids also produce gas, though to a much less degree than the physoclystids. 5 The so-called gas gland is the seat of gas liberation. The histology of the gas gland and its blood supply (rete mirabile) are dealt with. Experimental results indicate that a continuous liberation of gas takes place here and that in case of need there is additional activity of the gas gland controlled by the nervous system. 6 Gas resorption takes place in the “posterior gas organ” (oval), mainly by diffusion. But other parts of the swim-bladder wall are permeable to gases, particularly to carbon dioxide. 7 In conclusion the various theories put forward to explain gas secretion are critically discussed. Some workers assume that gas secretion actually takes place in the cells of the gas gland, forming, as they do, an epithelium lining the bladder. But more recently it has been maintained that the gas gland merely produces a particular secretion which passes into the blood capillaries, where it causes an increase in gas tension, particularly in the rete mirabile. This secretion is said to have an acid character, raising the carbonic acid tension and thus causing a rise in oxygen tension in the blood. In the rete mirabile, diffusion and repetitions of this process are said to bring about a rise in the oxygen tension of the blood until eventually oxygen passes by diffusion into the bladder. But there are arguments and experimental data which speak against the phenomena just described as being the sole mechanism, and which make it probable that this process of increase of oxygen pressure through a rise in carbon dioxide partial pressure has only a preparatory role, facilitating the process of secretion by the gas gland cells, through the breakdown of which oxygen and nitrogen are liberated against pressure into the swim-bladder.

Biochemistry of the lower fungi

Abstract: SUMMARY 1 The study of the biochemistry of the lower fungi received a great impetus from the classical researches of Wehmer begun in 1891 The more recent developments are here reviewed The biochemical characteristics of moulds often correspond closely with the taxonomic features and thus assist in classification 2 A medium suitable for mould growth must contain the elements sulphur, phosphorus, potassium, and (probably) magnesium Traces of certain heavy metals, namely iron, zinc, copper, and manganese, seem to be essential for the growth of Aspergillus mger and probably of other moulds 3 Combined nitrogen is also essential for growth and may be supplied in inorganic or organic form 4 The possible sources of carbon are very diverse, alcohols, carbohydrates and many organic acids being readily utilized 5 Although moulds are essentially aerobes, some species can tolerate a low oxygen tension Diminution in the oxygen supply may alter considerably the products of metabolism 6 Small amounts of certain organic substances specifically stimulate or inhibit some of the metabolic processes of moulds Vitamins of the B group have a favourable effect on growth and sporulation in the case of some species Certain moulds are able to elaborate substances inhibitory to other micro-organisms 7 The metabolic products are very varied in nature and range from the simpler plant acids (oxalic, fumaric, malic and citric acids), polyhydric alcohols and products of alcoholic fermentation to substances containing non-benzenoid rings such as derivatives of furane, pyrone, tetronic acid and cyclopentanone, substances containing benzenoid rings, such as derivatives of benzene, benzoquinone, anthraquinone and xanthone, pigments, sterols, fats, phospholipins and complex polysaccharides Vitamins of the B group and the provitamins A and D are also found amongst mould products In presence of arsenic, certain species such as Scopulariopsis brevicaulis produce volatile organic arsenical compounds Substances containing chlorine as part of the organic molecule are also synthesized from inorganic chlorides, and organic nitrogenous compounds including proteins from inorganic nitrogen Evidence is thus afforded for the outstanding synthetic activities of the lower fungi 8 Whilst the mechanism of synthesis is as yet an unsolved problem, the suggestion is advanced that some of the complex products may arise from the polysaccharides which are of such frequent occurrence in mould metabolism

Die messung und bedeutung der elektro‐lytischen polarisation im nerven

Abstract: SUMMARY The importance of polarization in the behaviour of electrically stimulated nerves can only be elucidated by experiments in which the effects of both polarization and stimulus are measured at the same time. With this in mind, both the resistance and the reactance of different nerves have been measured, sinusoidal alternating current covering a wide range of frequencies being used for stimulation. At the same time the dependence of current threshold on frequency has been investigated. Under certain conditions both the magnitude and the course of change of concentration (or of the change of charge) at the polarizable interfaces can be calculated from the resistance measurements. Supplementary measurements have been made with rectangular current impulses and condenser discharges. The result, in the case of the sciatic nerve of the frog, is that the behaviour of the current threshold at low frequencies can only be explained intelligibly by the assumption of a certain process taking place in the tissue, which, like the “accommodation” of Nernst and of Hill, raises the electrical requirements at low frequencies, although there is no increased loss at the polarizable interfaces. At frequencies about 200 cycles the effect of the stimulus is parallel to the quantity of electricity stored at the interface. However, the potential arising from this amount of electricity at the interface which is being studied is not at all constant at different frequencies. If the potential at the interface be supposed to be the decisive factor (Nernst), which is in fact the more satisfactory assumption, then the interfaces whose polarization is mainly being measured cannot be those at which the important processes take place. Other interfaces must lie behind them, storing without loss at higher frequencies. On the assumption that in non-medullated nerves the important interfaces are exposed and more easily accessible for measurement, corresponding measurements were carried out on nerves of Maja, Octopus and Aplysia. Compared with the sciatic nerve of the frog, all resistances and threshold values are shifted towards the lower frequencies by 101·5 to 102·5. In fact, the effect of the current appears to correspond better with the calculated potential at the interfaces. This potential would be 3–8 mV. The available data, however, are insufficient for final conclusions. The assumption of a process with a finite velocity, taking place in the tissue and caused by the electrical change, would give a satisfactory agreement between the potential theoretically deduced for constant potential at the interface and the experimentally established frequency relations to the current threshold at higher frequencies. In order to decide what is the influence of polarization on the behaviour of the current threshold at different frequencies, and what is to be attributed to processes taking place in the tissues, measurements under varied external conditions (length, temperature, electrolyte concentration, narcotics, poisons) will have to be carried out. Preliminary experiments show that both increase in the calcium content of the nerve and calcium decrease lead to a decrease in the total amount of polarization as compared with the normal. Calcium appears to act upon two different structures. The frequency relation of the current threshold, on the other hand, is affected by calcium in one way only. The current threshold is always raised by an increase in calcium, more so at high than at low frequencies, the minimum of the frequency curve being shifted towards the lower frequencies. Increase in potassium content leads to a decrease in polarization, the minimum of the current threshold being shifted towards the higher frequencies. Up to the present these results merely support the conclusion that, on low frequency stimulation of the nerve, a process taking place in the tissue can be separated from the factors that govern the processes at higher frequencies. It is probable, however, that further investigations will enable us to state more accurately how and to what extent the effect of polarization and the influence of secondary processes in the tissue are expressed in terms of the time relations of the processes caused by electrical stimulation.

Genetics in its application to plant breeding

Abstract: SUMMARY 1 The importance of Mendelism in relation to practical breeding problems is illustrated by reference to early work on the inheritance of economic characters. 2 Examples are given of improved varieties that have been produced by individual plant selection. The possibilities of success are shown to be dictated by the completeness of the material and one of the essentials for successful breeding is shown to be the collection of adequate and representative stocks of initial breeding material. This is illustrated largely by reference to Russian work, which has also elucidated the laws governing the distribution of plant varieties, characters and genes. 3 The possibilities of putting interspecific or distant crosses to practical use are analysed and cases where this has been done are cited. Chromosome duplication is shown to be a frequent phenomenon in such cases and to be a factor greatly increasing the economic value of such distant crosses. Numerous cases are quoted and the phenomenon is shown to have played an important role in the origin of new species and forms in nature. Its experimental control is thus of great practical value. 4 The origin of new forms of pathogenic fungi by hybridization and mutation is illustrated and shown to be a serious obstacle in breeding for disease resistance. 5 Examples are given where the obstacle has been overcome by breeding methods and other cases are mentioned where the problem of disease resistance remains unsolved. 6 The role of mutations in the origin of new forms of agricultural plants is discussed and the possibilities of effecting this process artificially are analysed. 7 The phenomenon of vernalization is described, with special reference to breeding. The significance of this and other recent physiological studies in producing forms possessed of earlier maturity is discussed. 8 The nature of plant yield is discussed and reference is made to attempts to analyse and regulate this by genetical methods.