400 CARNEGIE INSTITUTION OF WASHINGTON. 



for a longer period than many published researches have led us to 

 expect. This is in harmony with some of our earlier experiences before 

 the role of the vitamines was as well known as at present, and likewise 

 with the belief of some of the English investigators, who note that "the 

 animal organism normally contains reserve supplies of the factor A 

 in its own body," and that ''these reserves are mobilized for use when 

 a deficiency occurs in the diet, but as soon as they are exhausted growth 

 is immediately inhibited." It is possible that, as McCollum has 

 suggested, this difference in the time of survival can be attributed to the 

 animals rather than to the diets, our rats being perhaps more vigorous 

 than many of those used by others. 



At the present time uncertainty prevails regarding the effect of 

 heat upon the various vitamines. We have repeatedly pointed out 

 that heat as applied in the ordinary process of desiccation or cooking 

 does not noticeably affect the water-soluble vitamine. Our experi- 

 ence with the fat-soluble vitamine has not been in harmony with that 

 of certain other investigators who regard this food-factor as very 

 readily destroyed by heat. In view of the importance of the matter, 

 we are repeating these studies. Experiments still in progress have 

 confirmed our former experience respecting the failure of steam to 

 affect the potency of butter-fat as a source of the fat-soluble vitamine. 

 These have also shown that even heating in a dry oven at 100° C. for 

 as long as 16 hours does not greatly affect the efficiency of butter-fat 

 in restoring animals that are suffering from the effects of the lack of the 

 fat-soluble vitamine in their diet. We are not yet in a position to 

 assert that heat has no destructive action; but whatever, if any, may 

 occur is certainly not great. Why this food-factor has shown greater 

 stability in our hands than in that of other investigators we are not 

 yet prepared to explain. The most striking illustration of heat 

 stability which we can report at this time involves the at least tempor- 

 ary relief of animals with daily doses of 0.1 gm. of butter-fat heated 

 at 110° for 16 hours. Proceeding on the assumption of others that 

 prolonged heating in an oven will destroy the fat-soluble vitamine, 

 we have tested foods subjected to dry heating at 93° for 15 hours 

 without noting any striking deterioration. 



Practical feeding is concerned with the naturally occurring foods, 

 and for these many of our experiments have given some indication 

 of relative values. From the more purely scientific standpoint it is 

 desirable to know whether the need for the various vitamines is related 

 to the amount of active tissue, i. e., to the extent or intensity of the 

 metabolism, to the size and age of the animal, and whether these 

 needs vary absolutely or relatively under a variety of physiological 

 conditions. Accordingly we have begun a study of the minimum 

 quantities of brewery yeast required by animals of varying sizes and 

 stages of growth to develop normally. 



