摘要:

SummaryIn the past, largely on an empirical basis, it was found that the most effective liquid media for culturing animal tissue cells consisted of mixtures of physiological saline solutions, tissue extracts (preferably from embryonic tissue) and serum or plasma. The marked influx of investigators with primarily biochemical interests into the tissue culture field in the last few decades has led to determined efforts to learn more of the precise relationships between the composition of these media and the metabolism of the tissues. Since both of these are so complex, and the equilibrium between them is such a delicate one, it is perhaps not surprising that many apparently contradictory results are seen in the current literature.The place of physiological salt solutions in tissue cultures appears to be a relatively simple matter, and their functions are reasonably well understood. The present confusion relates to the role of the tissue extract and serum components of the medium. For certain types of cells there is evidence that a tissue‐extract nucleo‐protein fraction, supplemented by a surprisingly small group of smaller molecule nutrients, is adequate to support growth, at least for short periods. Various possible mixtures of these smaller components may be effective as a supplement in the same system, although it is probable that optimum combinations exist, again depending on the cell type and the culturing conditions. The tissue nucleoprotein fraction cannot be considered as a ‘growth hormone’, in the conventional sense of that term, since other cell types, or even superficially similar cell types taken from other animal donors, are able to maintain themselves satisfactorily when this fraction is completely absent, at least if serum proteins are present in the medium. It is thus evident that quantitative comparisons of data found by various researchers are of very dubious validity unless it is certain that identical culturing techniques were applied, using identical cell systems.On a more positive note, however, it seems probable that the analytical approach to the liquid medium problem is bringing the long‐sought goal of a controlled composition ‘synthetic’ medium for cultured animal cells much nearer to attainment for certain systems sharply defined as to cell type and culturing procedures.There are also indications that ‘growth’, biochemically speaking, as defined by the cell division in a culture, may be a separate process from ‘growth’ as defined by increase in culture mass, protein content or similar criteria. In other words, the chemical and physical conditions required to aid in inducing or in completing the mitotic cycle are not necessarily directly related to the nutritional requirements of growing and maturing individual cells in a healthy culture.There is some evidence that extracts made from tissues of older animals are, in many culture systems, as effective as extracts of embryonic tissue. Since, on the whole, such tissues are more accessible, their wider use by tissue culturists should be investigated more extensively.The role of serum in culture media is still not clear. In some cases it is apparently not required at all, in others it has a beneficial effect. Many of the reported contradictions as to the value or lack of value of serum in culture media are probably related to its variability in composition and state of preservation, and to the age and health of the donor animal. Until more experiments are done with better defined materials, resolving these conflicting results does not appear to be possible.A synthetic medium which would either fully support growth and development of all tissues, or one which would allow growth and development in limited but defined systems, is still the most logical goal as a reference medium and as the starting point for the systematic study of all phases of culture behaviour. The progress toward this goal has been definite but limited. With the tools now available for fractionating biological mixtures, synthesizing compounds of biological interest, and elucidating mechanisms of metabolism, the realization of a completely controlled medium, and possibly a completely synthetic medium, appears now to be merely a matter of time and continued effort. The advances in knowledge of tissue growth and behaviour that have already been achieved in the absence of such a medium are very impressive, and a constantly accelerating rate of significant research results is to be expected as the interest in

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb00593.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

SummaryThe organisms of the pleuropneumonia group, PPO, AGO and PPLO, constitute a uniform class of microbes. They all grow in small colonies, which can easily be overlooked unless inspected microscopically. Their colony form, a dark central portion embedded in the agar medium and lighter peripheral zone, is characteristic. Their morphology is fundamentally simple. Small granular forms, of the size of vaccinia virus, called minimal reproductive units, can initiate the growth of the larger forms. The organisms lack rigid cell walls, but have a flexible outer boundary (‘plasmalemma’). The shape and size of the organisms vary and depend on environmental conditions. Filamentous forms, small globules, disks and, on solid media, large flat forms are observed. Eventually, all these forms produce the minimal reproductive units.The nutritive requirements of the members of the group are rather exacting. Some grow well on ordinary media, but most of them require an additional factor derived from serum and some other growth factors as well. Suitable media are of paramount importance for the isolation and maintenance of these exacting organisms.Identification of organisms of the pleuropneumonia group in material from lesions by means of fixed and stained preparations is very difficult and liable to error. In most cases only the established culture on penicillin‐free media can be regarded as positive evidence of the presence of a PPLO in the specimen.For the identification of species the serological method is most reliable, though some organisms can be distinguished by their special growth characteristics.Pleuropneumonia organisms are killed by disinfectants, organic gold compounds, streptomycin and aureomycin, but not by sulphonamides and penicillin.Some varieties of organisms have been found in humid soil, in decaying plant material and in polluted water, and others have been isolated from the organs or body fluids of animals, or from their mucous membranes. Those that are known as causes of animal diseases, though widely varying in their effect on their hosts, show an interesting similarity in their mechanism of infection. Though the diseases produced are often devastating and lethal, infection in the field does not readily follow exposure to the infective agent. However, outbreaks of the disease often occur in animals exposed to stress, and it appears that these events light up inap‐parent infection acquired some time previously; that is to say, the infection becomes manifest when the resistance of the animal is lowered. This has been observed in the great epizootics of bovine pleuropneumonia and agalactia of sheep and goats, where the second factor may be fatigue or, in the case of sheep and goats, parturition and lactation. In laboratory animals also a natural latent infection may become active on application of unspecific substances or of a second infective agent, which may or may not be itself pathogenic for the injected animal.A new line of research has been opened by experiments on mixed infections. When the non‐mouse pathogens PPLO, PPO or AGO isolated from acute cases of disease are injected into these rodents, together with the mouse‐pathogenic ectro‐melia virus, an infection is produced which is more severe than the ectromelia infection alone. The organisms grow abundantly in the organs and exudates of the mice, and the mixed infection can be transferred from one mouse to the other by injection of organ emulsions or exudates. However, when an avirulent PPLO, PPO or AGO or a saprophytic organism is used, together with the ectromelia virus, the organisms are ingested by the phagocytes and killed. This laboratory phenomenon suggests that it may be profitable to search for a second factor or second infective agent in natural diseases associated with PPLO, when a causal relationship between the organism and the disease has not been established.It has been suggested that the organisms of the pleuropneumonia group may represent L phases of hypothetical bacteria. Though there is a morphological similarity between these two forms, evidence for such an assumption is so far lacking. It is possible to distinguish between the L phase of bacteria and genuine PPLO. Promotion of knowledge is better served if the two are regarded as distinct until evidence for a genetic relationship is forthcoming.Classification of the pleuropneumonia group of organisms seems premature. They are not bacteria proper, nor are they viruses. From the size of their minimal reproductive units, from their simple morphology and from their fastidiousness in regard to nutritive requirements, they may be regarded as forms intermediate between viruses

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb00594.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

SummaryA comparative study of woodlice which show different degrees of fitness for terrestrial life provides information about the evolution of land faunas and underlines the significance of water relations in this respect.Species of woodlice differ as regards rates of transpiration and survival in dry air. They may be considered as physical bodies so far as the effects of temperature and humidity upon evaporation are concerned, and they probably lack an epicuticular wax. No simple relation has been found between those climatic factors which affect evaporation and period of survival; neither is it expected on theoretical grounds.Transpiration from the region of the pleopods is greater, per unit area, than from elsewhere. Pseudotracheae assist respiration in dry air. In moist air oxygen is absorbed through regions of the integument other than the pleopods; but such integumental respiration decreases in importance in more terrestrial species.The only adaptation to land as regards excretion is a general suppression (compared with aquatic isopods) of nitrogen metabolism. Uric acid in small quantities is retained in the tissues. The faeces are moist. The tegumental glands are not an important source of water loss. The pleopods are not moistened by glandular secretions.Desiccated woodlice can restore their original weight by absorption of moisture, by mouth and anus, from free water surfaces, and by mouth from moist surfaces, even though the ambient air is unsaturated. The higher forms possess external capillary channels which assist in irrigation of the pleopods.The osmotic pressure of the blood ofLigia oceanicais higher than that of sea water; that of the other species measured is somewhat lower. Osmotic regulation is possible forLigiain dilute sea water down to 50%, but adaptation to land on the part of most woodlice seems to be secured by osmotic tolerance rather than regulation.Woodlice can withstand higher ambient temperatures, for short exposures, in air at 50% R.H. than in saturated air, and this is the result of rapid transpiration. In the field transpiration plays a significant part in determining body temperature, and may be of survival value during exposure to direct insolation.All species require saturated air or a moist substrate in their permanent habitats, and it is probable that they differ as regards tolerance of suboptimal conditions during wandering rather than dryness of the normal retreat. With this proviso the families which have been investigated stand substantially in the following order of increasing terrestrialness of habitat: Ligiidae, Trichoniscidae, Oniscidae, Porcel‐lionidae, Armadillidiidae. They also stand approximately in the same order as regards various morphological and physiological specializations associated with life on land (Table 1).What success the group has achieved on land may be ascribed to avoidance of the rigours of true terrestrial conditions by means of behavioural mechanisms which retain them in the cryptozoic niche, rather than to morphological or physiological adaptations.Further information is needed along three lines: (i) precise microclimatic measurements linked with observations of behaviour in the field, (ii) laboratory analysis of orientation mechanisms, (iii) neurophysiological investigation of the sensory mechanisms involved.The geological age of the group is uncertain, but there were probably land‐living oniscoids before the Tertiary. Their comparative lack of progress subsequently may be the result of retaining a water‐permeable integument, which is necessary for cooling during brief exposures to high temperatures and also for respir

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb00595.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

SummaryThe early development of an organism is a critical stage which many factors may influence unfavourably. Maternal nutritional deficiencies, especially vitamin deficiencies, can disturb the development and bring about the most diverse malformations, affecting the nervous system, eye, vascular system, kidneys, limbs, etc. The teratological effects of deficiencies in vitamin A, vitamin B2, pantothenic acid and folic acid are firmly established.Deficiencies not only produce malformations in the embryo. They may merely retard development, but they can also cause various lesions, and among others lesions which are analogous to those brought about in the adult by nutritional deficiencies.The gravity of the result of deficiencies varies greatly. It may be negligible or it may end in the death of the embryo or sterility of the mother. The effect is a function of the intensity of the deficiency, as shown by chemical estimations of the vitamin in question.A slight deficiency may produce a malformation. It may therefore occur readily, the more so as it may result from various causes, such as an insufficient exogenous or endogenous supply, a disequilibrium of the ration, imperfect utilization, etc.Deficiencies act on the embryo as on the adult, by a disturbance of metabolism, for it is known that many vitamins are essential constituents of enzymatic systems. The results of the deficiencies depend upon the tissues or cells with which these systems are specially concerned. At an early stage such metabolic disturbances may affect organizers and so cause anomalies in development, that is, deformities.Here, as elsewhere, genetical factors may intervene in restraining or facilitating the effect of a deficiency.It is probable that these phenomena, observed in several types of birds and mammals, are of general occurrence, to be found also in man and in domestic animals.From the practical point of view it follows that maternal nutrition should be closely supervised.

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb00596.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY