296 ANT^UAL REPORT SMITHSONIAN INSTITUTION, 1942 



is about 0.5 mg. per kilo. Using these values then, it would appear 

 that the nicotinic acid requirement of a human being is at least 

 15 mg. per day. Bacteriological methods have also recently been 

 developed for nicotinic acid determination and these procedures give 

 accurate results. By calculating the nicotinic acid content of an 

 average diet it would appear that it contains 15 to 20 mg. per daily 

 portion. As far as we know, there are no factors in the average diet 

 which tend to alter the nicotinic acid requirement, although in- 

 creased exercise may have a definite effect on the requirement of 

 this factor. 



The greatest limitation in the above figures is the lack of recogni- 

 tion of the less-known vitamins. Certainly the vitamin Ba require- 

 ment of a human being may be as important as any of the other 

 B vitamins. Yet we have no way of setting a specific figure at the 

 present time. We can only make a rough assumption that the vita- 

 min Be requirement is in the same order of magnitude as vitamin Bi. 



Pantothenic acid is undoubtedly required by the human being, but 

 at the present time we cannot even give quantitative figures for the 

 requirement of pantothenic acid in animals. Again the pantothenic 

 acid apparently affects the requirement of some of the unknown 

 members of the B complex in the animal; whether pantothenic acid 

 has a similar effect in human beings needs further study. 



Another factor which has received a great deal of attention in 

 animal work during the past year or two is choline. The serious 

 difficulties that an animal encounters when diets low in choline are 

 used certainly suggest that studies on the importance of choline in 

 the human dietary should be made. Here again we have an example 

 of how the variation in the amino acid content of our diet may 

 affect the choline requirement since a high methionine intake tends 

 to decrease the choline requirement and a high cystine intake tends 

 to increase the choline requirement. 



We must, of course, recognize that much of our information re- 

 garding the human requirements has come from animal experiments. 

 In fact if we had not relied upon animal work we would not have 

 much information at the present time. But if we use the results 

 from animals we must realize that there is great variation in the 

 requirements of different species. This was first recognized, of 

 course, in the case of vitamin C when rats failed to require vita- 

 min C while the human being, monkey, and guinea pig did. We 

 are finding more and more such discrepancies. The most interest- 

 ing perhaps is the variation in the nicotinic acid requirement in dif- 

 ferent species. The rat and chicken apparently do not need this 

 factor preformed, while the dog is very sensitive to a lack of this 

 factor. Apparently the human being and the dog are very similar 

 in their requirements for nicotinic acid. We are now finding that 



