243 



which arise more directly from faulty composition of the diet, either of the 

 infant or child, or of the mother during gestation or during the nursing 

 period. 



The most important changes in our viewpoint relating -to nutrition 

 are the result of a better understanding of the chemical conditions which 

 a diet must fulfill in order to promote growth, and of the specific dietary 

 properties of each of the more important natural foodstuffs which enter 

 into the diet of man. These have been acquired in great measure dur- 

 ing the last ten years, and have enabled investigators to plan diets having 

 but a single chemical fault. This fault may be chosen at will, or diets 

 can be prepared which are faulty in respect to two or three dietary fac- 

 tors, each of which is definite and definable. Moreover, it is now pos- 

 sible to adjust these diets so as to make the quality with respect to the 

 faulty factor or factors of any desired degree of intensity. By employing 

 such diets, derived from any of a number of sources from among our 

 natural foods, modified in special ways by the addition of purified food 

 substances such as protein, inorganic salts, special preparations contain- 

 ing one or another of the unidentified dietary factors, it has been possible 

 to conduct experiments on animals which have served to clarify our views 

 regarding the effects of faulty diet on health and on the life history of the 

 individual. 



It may be stated definitely that experimental studies on animals have 

 resulted in the definite imitation of so many of the conditions character- 

 istic of malnutrition in man, that there is no room for doubt that the effects 

 of deficient diets are the same in mammals generally. It has thus been 

 possible to produce in animals, by diets in which the nature of the chem- 

 ical fault is known, each of the deficiency diseases observed in man. This 

 has given us an understanding of the relation of the diet to disease which 

 has been a great revelation. This knowledge when applied to practical 

 dietetics will be of inestimable service to humanity by preventing such 

 conditions as arise through malnutrition. 



The experimental results obtained during the last few years by Miss 

 Simmonds and myself (a) (&) afford a basis for a full appreciation of the 

 effects of faulty diets of different types on the well-being of an animal. 

 These correlate so well with human experience that their bearing on the 

 planning of the diet for the preservation of health and vigor, is of great 

 service in educational work. They make evident that among the several 

 factors which operate to influence health, the diet stands first in impor- 

 tance. They show clearly how far, when all factors such as temperature, 

 illumination, ventilation and opportunity for exercise, are made uniform 

 for a large animal population, and when no inequality is afforded by 

 the surroundings for infection, the diet will determine the manner in 

 which a young animal will develop physically, and perform the functions 

 of adult life. A description of the experience of a large rat population in 



