McCOLLUM— RELATION OF DIET TO PELLAGRA. 47 



The results of experiments with grown men restricted to experi- 

 mental diets for a few weeks or months do not form a safe basis for 

 drawing conclusions as to the quality of the foods employed. Cer- 

 tain conclusions may be warranted from general observations on 

 children living on faulty diets, and important deductions may safely 

 be drawn from the experiences of large groups of people living upon 

 more or less restricted lists of foodstulTs. Beyond this we must be 

 guided in human nutrition by the results of animal experimentation, 

 in which the conditions can be made sufficiently rigid to bring into 

 stronger contrast the faults of certain types of diets as contrasted 

 with others. It is certain that the injurious efifects of certain die- 

 tary practices are very real and yet not promptly apparent. The 

 debilitating effects of faulty diets may vary in their severity from 

 such as will produce polyneuritis or xerophthalmia or scurvy within 

 a few weeks, at one extreme, to such as will cause nervousness and 

 restlessness in varying degree, susceptibility to disease, and the ac- 

 quisition of. all those characters such as roughness of the skin, thin- 

 ness and coarseness of hair, and attenuation of form which accom- 

 pany the process of aging at a distinctly greater rate than would be 

 the case were the diet of a highly satisfactory character. 



We have much evidence that in case there is a close approxima- 

 tion of the actual physiological minimum for any factor during 

 growth, such as one or more of the essential inorganic elements or 

 one of the unidentified dietary essentials, lack of ability to meet the 

 more strenuous demands of reproduction and the suckling of young 

 will be observed, and the tendency will be great for the individual 

 to be carried off suddenly either by disease, or, as frequently hap- 

 pens, by causes which are not readily determinable. 



All our experience with diets of low protein content have indi- 

 cated that animals do not remain in a state of optimum well-being 

 even when the content of protein is sufficiently high to maintain in 

 certain individuals the initial body weight over as much as lo per 

 cent, of the normal span of life. We believe that health and vigor 

 are promoted by a liberal intake of protein of good quality better 

 than by any diet in which there is a tendency towards parsimony 

 with respect to this dietary factory. It should not be lost sight of, 

 however, that there are other factors in nutrition which are of equal 



