摘要:

SummaryThe limits, in weight and chemical stability, of the group of substances referred to as large molecules are discussed and the range is arbitrarily taken as from particles unresolvable by the microscope to those with molecular weight 5000. A unit of molecular weight is proposed and its advantages are discussed in cases where the nature of the bonds holding a particle together is uncertain.Four distinct meanings that can be carried by the word pure are described, and examples are given of each type of purity.The types of observation generally made and presented as evidence that a substance is pure are considered under seven headings. Chemical analysis and crystallinity are the least reliable, and specific serological tests can only show the absence of contaminants whose presence is suspected. The measurement of end‐points, whether by serum precipitation or infection, is subject to several errors and can at best only indicate whether or not the major constituent of a preparation may be serologically active or infective.Electrophoresis, ultracentrifugation and studies based on the principles of the Phase Rule, i.e. solubility and partition measurements, give the most reliable evidence of purity at present available. Several reasons are given for thinking that even these methods may be fallibl

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1940.tb00945.x

出版商:Blackwell Publishing Ltd    

年代:1940

数据来源: WILEY

摘要:

Summary1. In the hydroids in general, andTubulariaandCorymorphain 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.

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1940.tb00946.x

出版商:Blackwell Publishing Ltd    

年代:1940

数据来源: WILEY

摘要:

Summary1. In most species oestrogens mainly stimulate mammary duct growth. In the guinea‐pig and goat they promote complete alveolar development. The mouse is the only animal in which treatment with progesterone has been found to promote mammary duct growth. In other species simultaneous treatment with oestrogens and progesterone is necessary for complete alveolar development. It is difficult to say whether or not oestrogensper secan promote alveolar development, because the adrenal cortex produces progesterone.2. Androgens cause duct and alveolar growth in some species.3. Some now believe that, under the influence of oestrogen, the anterior pituitary produces a “mammogenic” hormone which promotes mammary duct growth.4. The presence of the anterior pituitary is essential for the initiation and maintenance of lactation. The anterior lobe is believed to secrete a specific lactogenic hormone (prolactin), but other anterior lobe hormones probably participate in the control of normal lactation.5. Oestrogens may inhibit lactation during pregnancy, but it is probable that the pregnant uterus is also concerned in the inhibition.6. The adrenal‐cortical hormone is necessary for lactation, since adrenal‐ectomized animals do not lactate, and, further, prolactin will not initiate or maintain lactation in hypophysectomized animals unless corticosterone or adrenotrophic hormone is also given.7. The thyroid gland is essential for normal lactation: thyroxine stimulates nilk secretion in the cow.8. Posterior pituitary extracts cause emptying of the bovine udder but do not affect the formation of milk.9. Oestrogen treatment enriches milk in fatty and non‐fatty solids, and so does thyroxine treatment. Repeated injections of certain prolactin extracts increase the fat content of Cow's milk; certain other prolactin preparations increase the lactose content.10. No true secretory nerves innervate the mammary gland. Lactation is disturbed in the cat if the sympathetic chains are extirpated.11. The extraction of milk from the bovine udder depends on the reflex erection of udder tissues caused by stimulation of the teat, which also appears to cause the release of a lactogenic hormone or hormones from the hypophysis.12. The mammary gland synthesizes lactose from blood glucose and also, probably, lactic acid. It is also possible that blood amino acids are de‐aminated by the mammary gland and used for lactose synthesis.13. The precursor of milk fat is the neutral fat of the blood. The mammary gland probably oxidizes long‐chained fatty acids to the short‐chained acids of milk fat.14. It is improbable that milk protein arises from blood amino acids. Plasma proteins are probably utilized for the synthesis of caseinogen, the phosphorus coming from the blood inorganic phosphate.15. Various enzymes have been detected in active mammary tissue, which is a particularly rich source of the alkaline phosphomonoesterase. Changes in the secretory function of the mammary gland are usually accompanied by striking changes in the phosphomonoesteras

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1940.tb00947.x

出版商:Blackwell Publishing Ltd    

年代:1940

数据来源: WILEY