148 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 4 



consumed in almost infinitesimal amoimts may, each in its way, be as 

 essential as those which form the bulk of any adequate dietary. This 

 complexity in its demands will, after all, not surprise those who have 

 in mind the complexity of events in the diverse living tissues of the 

 body. 



My earlier reference to vitamins, which had somewhat different 

 bearings, was, I am sure, not necessary for a reminder of their nutri- 

 tional importance. Owing to abundance of all kinds of advertise- 

 ment vitamins are discussed in the drawing room as well as in the 

 dining room, and also, though not so much, in the nursery, while 

 at present perhaps not enough in the kitchen. Unfortunately, 

 among the uninformed their importance in nutrition is not always 

 viewed with discrimination. Some seem to think nowadays that if 

 the vitamin supply is secured the rest of the dietary may be left to 

 chance, while others suppose that they are things so good that we 

 cannot have too much of them. Needless to say, neither assumption 

 is true. With regard to the second indeed it is desirable, now that 

 vitamin concentrates are on the market and much advertised, to 

 remember that excess of a vitamin may be harmful. In the case of 

 that labeled D at least we have definite evidence of this. Neverthe- 

 less, the claim that every known vitamin has highly important 

 niutritional functions is supported by evidence which continues to 

 grow. It is probable, but perhaps not yet certain, that the human 

 body requires all that are known. 



The importance of detail is no less in evidence when the demands 

 of the body for a right mineral supply are considered. A proper 

 balance among the salts which are consumed in quantity is here of 

 prime importance, but that certain elements which ordinary foods 

 contain in minute amounts are indispensable in such amounts is 

 becoming sure. To take but a single instance: the necessity of a 

 trace of copper, which exercises somewhere in the body an indis- 

 pensable catalytic influence on metabolism, is as essential in its waj' 

 as much larger supplies of calcium, magnesium, potassium, or iron. 

 Those in close touch with experimental studies continually receive 

 hints that factors still unknown contribute to normal nutrition, and 

 those who deal with human dietaries from a scientific standpoint 

 know that an ideal diet cannot yet be defined. This reference to 

 nutritional studies is indeed mainly meant to assure you that the 

 great attention they are receiving is fully justified. No one here, 

 I think, will be impressed with the argument that because the human 

 race has survived till now in complete ignorance of all such details 

 the knowledge being won must have academic interest alone. This 

 line of argument is very old and never right. 



One thing I am sure may be claimed for the growing enlight- 

 ment concerning human nutrition and the recent recognition of its 



