88 THE VITAMINS 



in practically undiminished proportion. Tso (1926) has reported that 

 Chinese preserved duck's eggs, "pidan," are apparently as rich in vita- 

 mins A and D as fresh duck's eggs, but are practically devoid of 

 vitamin B, showing that the process used in preservation has destroyed 

 vitamin B, doubtless through its strong alkalinity. Hoagland and Lee 

 (1924) have reported a possible slight destruction in the antineuritic 

 vitamin of eggs as the result of 7 minutes' boiling. 



Milk. — The mammary gland is believed not to synthesize the vitamin 

 but to take it from the blood, or through the blood from the tissues, of 

 the mother and convey it to the young through the milk. Since the 

 total amount of vitamin B available in the tissues is relatively small 

 the concentration in which it appears in the milk is largely dependent 

 upon the vitamin content of the mother's food ; or upon the bacterial 

 synthesis of this vitamin in the rumen of the cow (Bechdel et al., 1928). 

 This doubtless is one reason that different investigators have received 

 different impressions as regards the richness of milk in this vitamin. 

 Another reason is to be found in the observation of Osborne and 

 Mendel (1918c) that individual animals vary in their requirements for 

 vitamin B ; and still another in the differing lengths of experiments 

 and criteria of satisfactory growth. In some cases the experiment has 

 been considered successful and the food satisfactory when growth at a 

 nearly average rate was maintained for a few weeks, while other in- 

 vestigators, such as Osborne and Mendel, have discussed the question 

 in terms of the requirement for optimal growth. If, to a basal ration, 

 milk is added in increasing proportions, it is probable that the diet, 

 even though adequate before, will be improved by the increased pro- 

 portion of milk in other respects as well as in its content of vitamin 

 B, and so the experimenter may be led to the use of more milk than is 

 really necessary to supply the needed amount of vitamin B. From a 

 study of the work of various investigators it appears that milk solids 

 contain about as much vitamin B as the solids of eggs and much more 

 than the solids of ordinary meat; and that, on the average, an amount 

 of milk sufficient to furnish from 10 to 20 per cent of the total solids 

 or total calories of the diet will furnish as much vitamin B as is needed 

 to make the food mixture adequate for growth. 



Commercially dried milks appear to be practically as rich in vitamin 

 B as the solids of the original milk. Dutcher and Francis (1926), from 

 a study of the vitamin B content of evaporated milk made by the 

 vacuum and aeration processes from milk, the original vitamin B con- 

 tent of which was determined, concluded "that vitamin B is not readily 

 destroyed by the evaporation method described and only under unusual 



