GROWTH AND NUTRITION 99 



and fats in the diets ; and with the requirement for the un- 

 identified nutrients, the vitamins. There is another aspect to 

 nutrition, however, that of quantity, and for many years this 

 phase of nutrition was the predominating one. The chief sub- 

 ject of nutritional investigations was the quantity of total nu- 

 trients required by the animal organism, or, perhaps more spe- 

 cifically, the total quantity of energy. During recent years this 

 phase has been overshadowed by qualitative considerations, be- 

 cause of the newer developments in this respect. While it is 

 necessary to recognize the unique importance of individual con- 

 stituents of the diet, yet it is imperative to remember that nu- 

 trients must also be considered as a total, the entire quantity of 

 food must at least equal a physiological minimum. 



It is a general belief held by most practical live-stock pro- 

 ducers, that superior individuals can only be obtained if they 

 are fed liberally from birth to maturity, and that temporary 

 retardation of growth may result in permanent stunting, at least 

 to some degree. Obviously undernutrition may not mean the 

 same thing in all cases ; so this phase may be considered from 

 different aspects. Thus undernutrition is affected by the age at 

 which underfeeding occurs, by the length of the underfeeding 

 period, and possibly by the kind of underfeeding, that is, quali- 

 tative or quantitative. Thus the supply of food may be ample, 

 but of a kind that will not permit normal nutrition. The next 

 point of interest then is what may be the effects of various kinds 

 and degrees of underfeeding. 



Obviously these phases must overlap somewhat, and it is im- 

 possible to study any one uncomplicated by other factors. As 

 the first case, however, we shall consider one in which an at- 

 tempt is made to inhibit all growth. We may suppose that at 

 weaning time, or earlier if practicable, food is partially with- 

 held from an animal so there is no further increase in weight. 

 As will be shown later, growth does not necessarily cease when 

 gains in weight cease. This means then that there may be an in- 

 crease in the structural units proper of the body, in protein, in 



