226 THE V1TAMINES 



diet. If growth ensues, it may be concluded that the basal diet 

 was insufficiently purified. Older animals, weighing over 100 grams 

 should not be used since the vitamine A requirement diminishes 

 with age. If the growth remains stationary during 10 to 14 days, 

 the substance to be tested may be added, preferably apart from the 

 diet. If growth is seen, it may be concluded that vitamine A was 

 present in the substance added. 



Significance of vitamine A in physiology and pathology. From a 

 study of this vitamine in various nuts, Coward and Drummond (605) 

 came to the conclusion that it occurs only in small amounts in seeds, 

 but that during the process of germination it appears in greater 

 quantities. We have already mentioned the possibility that green 

 leaves may synthetize vitamine A under the influence of sunlight, 

 and in this connection Delf (605a) has found that the inner white 

 leaves of cabbage are free from this vitamine, while the outer green 

 leaves contain the substance. Recently, Coward and Drummond 

 (605b) have experimentally substantiated these findings, showing 

 that green leaves form vitamine A only in the presence of sunlight, 

 while the lower organisms devoid of chlorophyll are unable to syn- 

 thetize this vitamine. 



Hughes (605c) fed a number of animals on diets rich and poor in 

 vitamine A, but on examination of the organs, no relation could be 

 shown between the vitamine A content of the food and that of the 

 adipose tissue. Drummond, Golding, Zilva and Coward (605d) 

 explain the poverty of pig's fat in vitamine A in two ways (1) inade- 

 quacy of the diet in this substance, and (2) losses by oxidation during 

 the melting out process of the fat. 



We have already stated that the lack of vitamine A in rats is fol- 

 lowed by no characteristic pathological changes, and hence it is 

 difficult to point out just what is the importance of this substance. 

 Drummond (606) tried to solve this question. Since this substance 

 is associated with fats, as a rule, it was easiest to assume that it 

 played a part in the fat metabolism, but it was not possible to find 

 such a relationship. Rats lacking both this vitamine and fat showed 

 no different behavior from those animals lacking only one of these 

 constituents. The temperature of these rats was normal, so that 

 this substance has nothing to do with the regulation of body tem- 

 perature. In another experiment, Drummond tried to see whether 

 or not vitamine A plays a role in the synthesis of neutral fats from 



