bluuebunny/crossref_metadata_2025_split huggingface dataset:
AQUATIC AND AERIAL RESPIRATION IN ANIMALS
Authors: CARTER G. S. 
Published: January 2008

Summary1. The physical conditions governing respiratory exchange across epithelia exposed to water and air are considered, and the efficiency of aerial and aquatic types of respiration are compared. The effects of the known differences in the dissociation curves of the various respiratory pigments which occur in animals are discussed.2. The changes which have taken place in the respiratory organs of animals possessing aerial respiration, but belonging to groups of which the majority of the species are aquatic, are reviewed.3. From the previous discussion of the physical conditions of respiration, it is concluded that respiration in water should be more efficient than in air, if the structure of the respiratory epithelia are similar. It is found that a comparison between the area of respiratory epithelium in organs of aerial and aquatic respiration in the vertebrates supports this conclusion.4. The suggestion is made that the relative ease with which invertebrates, such as the Molluscs and Crustaceans, can pass from water to land as compared with the vertebrates is due, at least in part, to the value of the tension of loading of haemocyanin, which is lower than that of the types of haemoglobin contained in corpuscles, which are found in the organs of aerial respiration of the vertebrates.5. The apparently greater efficiency of some forms of cutaneous respiration in air than in water is considered, and is found to be due to secondary factors. It is suggested that one condition which has permitted the large size of some animals, possessing no restricted organ of respiration, such as some of the Oligochaetes, is the presence of haemoglobin in solution. The tension of loading of this pigment is much lower than that of any other respiratory pigment.6. The reason why the majority of terrestrial animals have reached the land through the fresh waters rather than directly from the sea is discussed. The suggestion is made that this has been partly caused by the favourable series of inter‐mediate environments between the fresh waters and the land, and that the evolution of many of the numerous adaptations necessary for terrestrial life has been induced in these environments serially, and therefore with much greater ease. The much greater variability of the fresh‐water environments has also undoubtedly been important in producing this result. The importance of the tide in maintaining the constancy of conditions on the marine littoral is emphasised.
THE TIME FACTOR IN ELECTRICAL EXCITATION
Authors: RUSHTON. W. A. H. 
Published: January 2008

Summary.The rate of development of the excitatory process in tissues may conveniently be characterised by a measure, the “Excitation Time,” which was formerly known as “Chronaxie.” This constant also measures roughly the rate of other processes in the tissue, e.g. action‐potential wave, conduction velocity, rate of contraction, etc. probably because all these processes are limited by the development of electrical states in the tissue.The excitation time of muscle (but not medullated nerve) is very largely dependent on the size of the electrodes used. This is easily explained in terms of a physical theory of excitation. If nerves are stimulated by the penetration of current through the nodes of Ranvier, these will constitute unvarying pore electrodes and account for the relative independence of nerve upon electrode size.According to Lapicque, paralysis by curare and other similar conditions is due to a great increase in chronaxie of the muscle, which initially was the same as that of the nerve. This standpoint, which is fundamental in Lapicque's school, is criticised in detail. In the first place, the evidence upon which the theory rests is inadequate, In the second, further work by Lapicque's school has rendered the theory so complicated that it is now of doubtful practical value. Lastly, the experiments of other workers appear to make the theory untenable.In the light of the rejection of Lapicque's views and of the dependence of excitation time upon the nature of the electrodes, it is necessary to review the significance of the measure, and to modify the technique of its determination. Some practical aspects are discussed, and it is pointed out that at present the chief application to biology is in the analysis of multiple excitabilities (e.g. muscle with nerve twigs, tonic and phasic muscles, etc.). But it must be emphasised that in this analysis it is essential to determine the whole strength‐duration curve if the results are to be significant.
THE PROCESS OF REGENERATION IN HYDROIDS
Authors: BARTH L. G. 
Published: January 2008

Summary1. In the hydroids in general, and Tubularia and Corymorpha in particular, the stimulus for regeneration involves two factors: (1) removal of dominance exerted by either the fully formed hydranth or a regenerating hydranth, and (2) the presence of a gradient of oxygen at a localized region of the stem or a mass of cells isolated from the stem.2. Dominance, or the inhibitory effect of a regenerating region, can be explained either on the basis of electrical differences in potential which produce chemical inhibition, or as the competition of regions of the stem for hypothetical substances circulating in the stem and necessary for regeneration. As yet no single experiment has decided between these two explanations of dominance and both should be subjects for investigation.3. The regional differences in rate of regeneration are correlated with regional differences in the rate of oxygen consumption of the stem, and the rate of regeneration can be varied by varying the oxygen consumption of the stem. These regional differences in oxygen consumption are due to differences in the resting stem and are not caused by the regional differences in regeneration.4. Since the stimulus for regeneration can be traced to an oxygen gradient, which results in an oxygen consumption gradient in the tissues, there is little value in speaking of an organizer in hydranth formation. Any agent which will bring about the above conditions will be an organizer. It is, therefore, possible to speak of the following as organizers: (1) oxygen locally applied, (2) tissues that have a higher oxygen consumption than the surroundings, and, perhaps, (3) respiratory catalysts, when their effects are investigated. On the whole, it would be better to speak of the coenosarc as organizing itself in response to a stimulus. The manner in which the tissue responds by cell movements and change in form is, of course, entirely unknown.
THE NUTRITION OF THE PROTOZOA
Authors: DOYLE WM. L. 
Published: January 2008

SummaryThe principal feature of recent studies on the nutrition of the Protozoa has been the development of culture media suitable for the maintenance of several score of species in ‘pure culture’. As investigators approached precise definition of the constitution of the culture media the significance of ‘trace elements’, accessory food factors and the like became more apparent. The types of culture apparatus, the methods of sterilization of organism and medium, the procedures of estimating growth of populations, and the exact composition of reagents have all been found to be of greater importance than originally realized. Within the phylum there exist chlorophyll‐bearing, plant‐like forms and numerous intermediary types up to and including those requiring living particulate food, thus providing the full range of nutritional types. The older systems of physiological classification have been extensively revised, but none of those proposed is adequate. In some instances the relations between variations in cytoplasmic structure (plastids) and nutritional requirements have been demonstrated.Many species of chlorophyll‐bearing and colourless flagellates have been studied. Intensive work on Polytoma, Chilomonas and Euglena has revealed notable species and strain variations with respect to factors such as fatty acid metabolism, nitrogen requirements, the effects of light on nutrient requirements and on response to plant hormones and vitamin constituents. The effect of systematic modification of chemical structure on the utilization of vitamin components has been studied for some species. A few dozen of the normally phagotrophic (holozoic) forms have been grown in the absence of other living forms (pure liquid culture), while certain forms have been grown on single species of food organisms (pure mixed culture) or on dead food organisms. With the exception of certain amoebae the salient work on pure culture has been carried out with the smaller ciliates, particularly Glaucoma. The media employed (protein hydrplysates, tissue autolysates, etc.) are chemically and physically highly complex. Such media contain labile constituents susceptible to important changes when subjected to minor procedural variations. Analyses of the media before and after the growth of organisms have given some indications of the nature of the nitrogenous fractions metabolized. The accessory growth‐factor requirements of these forms are complex. The very specialized nutrients required by parasitic forms have demonstrated interesting evolutionary relationships. An increasing number of biochemical experiments is being reported on the existence of various enzyme systems in the Protozoa. Our knowledge, however, of the metabolism of representative Protozoa remains fragmentary.
SPECTROGRAPHIC ANALYSIS OF PLANTS AND SOILS
Authors: MITCHELL R. L. 
Published: January 2008

SummarySpectrographic methods which are applicable to the analysis of plants and soils include those employing flame, arc and spark excitation. Some seventy elements can be determined spectrographically, the most important exceptions being gaseous and non‐metallic elements.The most widely used flame emission method is that devised by Lundegårdh, in which the solution under examination is sprayed into an air‐acetylene flame. This method is particularly suited to the determination of the alkali and alkaline earth metals in soil and plant extracts. The Ramage method, in which the material is introduced on a paper spill, has also been used to some extent.Arc methods are widely employed for the determination of both trace and major constituents, generally with solid material in carbon or graphite electrodes of a shape chosen to suit the object of the investigation. The most sensitive source for most elements is probably the cathode‐layer arc, although the high‐voltage a.c. arc is useful for certain elements in solution. Interrupted arc and spark sources have been less widely used but have advantages for certain purposes, such as the determination of boron.Some direct photometric methods, omitting the use of a photographic plate, are described.Spectrographic methods are applicable to qualitative, semi‐quantitative or quantitative determinations. Semi‐quantitative methods generally employ a visual or subjective assessment of the content of an element, and are useful in giving a general indication of the levels of most of the trace constituents present in any sample, with an accuracy of some 30%. When objective photometric measurements are used, figures reproducible to ± 3–10% may be expected, depending on the method employed and the element being determined.Applications of spectrographic methods to analyses of soils and plants have been along both lines, either the semi‐quantitative survey of as many elements as possible, or the quantitative determination of specific elements. Attention is drawn to the relationship of the soil content to the geological origin of its parent material and to soil effects which may influence plant uptake.
L'ACÉTYLCHOLINE ET L'ADRÉNALINE CHEZ LES INVERTÉBRÉS
Authors: BACQ Par Z. M. 
Published: January 2008

Résumé1o. Le tableau 2 résume ce que l'on sait sur la présence ďacétylcholine et de cholinestérase chez les Invertébrés, ainsi que sur la sensibilityé. des tissus àľacétylcholine et aux poisons qui paralysent ľaction de cette substance.2o. La présence de nerfs cholinergiques est démontrée chez les Annélides (Armicolu, Aphrodite, Lumbricus, Hirudo), et les Siponculiens (Sipuncuh), chez les 1 Iolot huries, chez un seul mollusque (Venus mercenaria).3o. Ľexistence de nerfs cholinergiques est inconcevable chez les Cœntérés.4o. Chez les Arthropodes (Crustacés, Insectes et Arachnomorphes) tout porte à croire que les nerfs ne transmettent pas ľ'excitation par ľintermédiaire ľacétykholine.5o. Chez leo Mollusques, àľexception de Venus mercenaria, tous, les essais de démonstration de nerfs cholinergiques ont échoué.6o. Ľexistence de nerfs adrénergiques chez les Annélides est très probable, mais non encore certaine; de tels nerfs existent vraisemblablement chez les Céphalopodes et chez ľaplysie.7o. Le cmur et les tissus des Invertébrés manifestent pour ľadrénaline et les amines syrnpathicomimétiques une sensibilityé non spécifique, le plus souvent faibie.
THE STRUCTURE OF THE STRIATED MUSCLE FIBRE
Authors: BARER ROBERT 
Published: January 2008

Summary1. The muscle fibre is regarded as a bundle of myofibrils, embedded in a viscous matrix, the sarcoplasm, the whole being surrounded by a delicate sheath, the sarcolemma.2. The sarcolemma is a thin, apparently structureless membrane. Preliminary study with the electron microscope suggests that it may be less than o‐i /u. thick. No fibrils can be seen with the electron microscope, but a large number of small nodules lie scattered over the membrane. The sarcolemma is probably not collagenous in nature.3. The sarcoplasm is a viscous, protein‐containing gel which surrounds the myofibrils. Mitochondria, glycogen and fat droplets are scattered throughout the sarcoplasm. Several enzymes have been isolated from what is believed to be the sarcoplasm. This suggests that the latter may be the site of important metabolic activity. The question of sarcoplasmic contractility is not yet settled. There is good evidence that it may occur in certain cells (myoblasts, striated fibres of tadpoles and insect larvae).4. The evidence in favour of the existence of myofibrils as contractile units is discussed. The fact that individual myofibrils or groups of myofibrils can be made to contract independently, and sometimes asynchronously, is strong support for this view.5. The electron microscope shows that the myofibrils consist of relatively straight protein chains. Several different striations (A, I, Z, M, N, H) can be recognized. There is no gross difference in orientation between the protein chains in the various bands, nor is there any evidence of a spiral structure.6. Several aspects of Szent‐Gyorgyi's work are discussed. While this work has led to a better understanding of the muscle proteins, the theories of muscle structure arising from it have found no general acceptance.7. Other theories attempting to account for the existence of the cross‐striations are reviewed. It is suggested that there is a periodic distribution of different chemical substances in the different bands. This may affect the physical, mechanical, and chemical properties of the myosin in those bands, and may account for the differences in birefringence between the A and I bands.8. Evidence is presented against the existence of a Z ‘ membrane’ or other transverse membranes uniting the myofibrils. No structural connexion is believed to exist between the sarcolemma and the underlying sarcoplasm and myofibrils. The relationship may be a purely viscous or frictional one.9. Reasons are suggested for the perfect alinement of the striations in neighbouring myofibrils. A full explanation may only be possible as a result of a better understanding of intermolecular and colloidal forces.
CAROTENOIDS AND REPRODUCTION
Authors: GOODWIN T. W. 
Published: January 2008

Summary.After a brief discussion of the essential chemical properties of carotenoids, the identification, occurrence and distribution of the pigments in the gonads and related organs of plants and animals have been reviewed. The information available concerning the metabolism of carotenoids in reproductive tissues and their possible function in reproduction has also been reviewed systematically.In the higher plants, as maturation proceeds the carotenoid content of the tissues decreases, owing probably to the redirection of carotenoid synthesis into the reproductive organs. Further, the synthetic mechanism itself must be altered in some way because new carotenoids, never encountered in leaves, are produced in the reproductive organs. There is no evidence that carotenoids are involved in fertilization. In fact, many pollens contain no carotenoids.Differential distribution of carotenoids in male and female gametes is encountered in some species of both algae and fungi, but whereas nothing is known about carotenoid metabolism and function in relation to reproduction in fungi, it is claimed that appropriate mixtures of stable and labile crocetin dimethyl esters stimulate both male and female gametogenesis in the alga Chlamydomonas.In aquatic animals carotenoids are actively mobilized into the gonads during sexual reproductive activity, and in some cases are rendered water‐soluble by attachment to proteins. Carotenoids do not appear to be necessary for normal embryonic development, but one report indicates their possible importance as fertilization hormones. Carotenoids may be present in the gonads to ensure that the larvae are adequately equipped for chromatophore responses. Changes in general coloration associated with sexual activity are also often mediated through carotenoids; in the case of the fish Cyclopterus lumpus, for example, astaxanthin appears in the skin in large amounts during the summer spawning period. Similar changes can be observed in some insects, for instance, the bright yellow colour of sexually mature locusts is due to accumulation of β‐carotene in the cuticle.In mammals which store carotenoids, these pigments undergo metabolic changes associated with parturition, but as not all mammals store carotenoids, and since many similar changes occur with vitamin A, it is doubtful whether the carotenoids are of significance per se.Although carotenoids appear to be unnecessary for the normal development of birds in both the pre‐ and post‐embryonic stages, they are actively mobilized into birds' eggs. They may, however, be necessary for optimum conditions of fertilization by increasing the sperm competitive ability of cocks, i.e. when hens are inseminated with an equal mixture of spermatozoa from cocks on an adequate diet and those on a lutein‐deficient diet, a larger proportion of offspring are produced from the normal group than from the lutein‐deficient group.
CEPHALOPOD PHYLOGENY AND CLASSIFICATION
Authors: DONOVAN D. T. 
Published: January 2008

Summary1. A mode of origin of cephalopod buoyancy, by withdrawal of the animal from the apex of the shell followed by withdrawal of liquid from the resulting space, is suggested.2. Buoyancy, once evolved, gave cephalopods an immediate advantage over contemporary animals and evolutionary radiation in the early Ordovician was a consequence of this.3. The earliest cephalopods probably had curved (cyrtocone) shells. Tightly coiled shells evolved from cyrtocones in at least two separate lineages and were in the first place adapted to a benthonic existence. Straight shells (orthocones) were adapted for efficient swimming. They usually had apical counterweights to maintain a horizontal position, but in forms without counterweights, liquid‐filled chambers could have served the same purpose.4. Six evolutionary branches are described, which were distinct by the end of the Canadian (Lower Ordovician). Each branch is believed to be monophyletic, and up to a point each is characterized by certain structures or trends.5. Increased efficiency in jet propulsion became possible in one orthocone group, consequent on loss of the ventral wall of the body‐chamber, so that the mantle cavity wall could become muscular and contractile. This group gave rise to the living di‐branchiates, or Coleoidea.6. The primitive septum, which was concave forwards, remained standard in most orthocones and in some coiled shells. Folded septal edges, giving rise to more or less complex septal sutures, evolved independently in a number of coiled lineages. Their significance is unknown.7. The siphuncle is simple and small in all coiled shells and in some orthocones. In some cyrtocones and other orthocones large siphuncles of complex structure were evolved. They usually contain deposits which are interpreted as counterweights.8. Existing classifications of cephalopoda stem from subdivisions recognized in the nineteenth century when knowledge of fossils was inadequate. They are ill‐balanced and should be abandoned.9. A classification based on phylogeny is now possible. The six branches already described may be regarded as major subdivisions. In addition, it may be desirable to subdivide branches on the basis of important evolutionary changes. The strongest case is for the separation of Coleoidea on the grounds of the loss of the shell.
THE SURVIVAL OF FUNGAL SCLEROTIA UNDER ADVERSE ENVIRONMENTAL CONDITIONS
Authors: WILLETTS H. J. 
Published: January 2008

Summary1. Sclerotia have been found to survive under adverse environmental conditions for long periods. Their viability is retained at low and subzero temperatures, while it is progressively reduced at temperatures above about 15° C. Dry conditions and lack of competition from other organisms favour survival. Depletion of food reserves results in loss of resistance to environmental factors.2. The majority of sclerotia consist of an outer layer of thickened, close‐fitting, often pigmented cells that form a rind over a tissue of closely interwoven hyphae. A cortex and medulla is often discernible.3. Features of sclerotia that are important in overcoming the harmful effects of desiccation and extremes of temperature include: the presence of a rind and sometimes an additional covering of either fungal or host tissue; the compact nature of the sclerotium; miscellaneous protectants on the surface of and in the hyphae; melanized hyphal walls; high intracellular osmotic concentrations; slow air‐drying to lower moisture content. Also the buffering action of the soil and the protection afforded by vegetation and plant debris are important.4. The active exudation of water, the accumulation and secretion of soluble carbohydrates during sclerotium development and maturation, and the formation of large amounts of mucilage are of significance in resistance to desiccation, extremes of temperature and radiations.5. The nature and the pigmentation of the rind together with the site of sclerotium development may give protection against harmful radiations.6. The loss of sclerotium viability caused by toxic chemicals in the soil and atmosphere or by the enzymic activities of other organisms is reduced by the rind and the melanization of hyphal walls.7. Survival under starvation conditions is achieved by the accumulation of abundant food reserves (lipids and/or carbohydrates) and a low level of metabolic activity. In the presence of a compatible host exogenous sources of energy are sometimes used.8. Although the sclerotium is highly adapted to survive adverse conditions for long periods, sometimes micro‐environmental conditions may be so severe that only a few sclerotia can retain their viability. However, even a few such comparatively large bodies, rich in food reserves, have a considerable inoculum potential.