NUTRITION AND GROWTH: I. 5 



I 



In view of the preceding considerations, it seemed quite interesting 

 and promising tliorouglily to study the influence of variations in the 

 quantity of food, and more especially of a restricted diet, on the growth 

 and development of mammals. 



To solve this problem, we must first study the conditions surrounding 

 the suppression of growth when the animal is at a standstill, receiving 

 only the amount of food required for existence without growth. We 

 must further endeavor to deteiTQine the maximum quantity of food which 

 can be given without causing growth, and in what way varying additional 

 amounts of food are used in the fonmation of new body substances. 



A number of questions at once arise. Can we, by the restriction of 

 food, suppress the process of growth entirely and, if so, for how long? 

 If we suppress the growth, does the animal lose its "tendency to grow" 

 as it ages ? Does the capability for growing depend on the age, or on 

 the size and weight of the animal? Is the growth of all parts of the 

 body suppressed to the same degree, or is the "tendency to grow" of 

 the various parts or organs of the body different? Do some parts 

 develop or grow at the expense of the rest? It is known that in a 

 starving animal the most important parts of the body, such as the 

 heart and brain, suffer relatively much less loss in weight than do 

 those of minor vital importance, namely, fat, muscles, and digestive 

 glands. If different parts of the body do have a marked difference in 

 the "tendency to grow," we shall be able to recognize this difference by 

 suppressing the growth for a time. 



The simplest and most usual method of estimating growth is by 

 controlling the live weight. A constant increase in weight is conclusive 

 evidence of the normal gTowth of a young animal. Some other indica- 

 tions of growth are increase in length and in other dimensions and 

 certain changes which relate to the stage of development. 



If the body weight remains constant, does this fact indicate that no 

 growth is taking place? Growth, as we imderstand it from a biologic 

 standpoint and in its relation to energy, constitutes a general, more 

 or less equal, increase of all parts of the body. jSTo growth means no 

 change whatsoever in the body. 



However, the live weight of an animal may not change at all, while 

 internal relative "changes between the different parts of the body," of 

 which I have already spoken, may take place. Obviously a constant 

 live weight is not an indication of lack of growth in our sense. The 

 question as to how far increase or constancy of live weight runs parallel 

 with growth or cessation of growth is important and of practical value 

 and deserves close attention. On the basis of these considerations the 

 experiments to be undertaken may be outlined as follows. 



A number of comparable animals must serve for each series of ex- 

 periments, one of them receiving just enough food to keep its body weight 



