DISTURBANCES OF GROWTH 247 



It is perhaps most convenient to discuss in this connection the effects 

 of undernutrition, in the sense of lack of sufficient food to meet the caloric 

 needs of the body, as well as a relative lack of sufficient amounts of -sev- 

 eral dietary factors due to restriction of the intake of food. Such studies 

 have been carried out by Aron (a) with dogs, and by Waters (a) and Trow- 

 bridge(a) with cattle. 



In Aron's experiments young pups from the same litter were divided 

 into experimental groups, one of which was fed liberally on a mixed diet, 

 so as to cause at least approximately optimum development. The other 

 group was fed the same diet, but the amount of food was adjusted so as 

 to maintain the body weights constant for about a year. The control 

 animals trebled their weights during this interval. The results indicate 

 that when the food supply is inadequate in amount .but satisfactory in 

 quality for the maintenance of nutrition at a plane at which there can be 

 no increase in weight, the body is not merely in a condition in which 

 there is lack of growth, but of starvation, and is actually undergoing 

 changes in composition in which a portion of the fat and muscle tissue com- 

 ponents disappear and are replaced by water. When increase in weight 

 is inhibited by restriction of the food supply, the skeleton grows at the 

 expense of certain of the soft tissues, especially the muscles. There is 

 therefore, a pronounced alteration of form, but the glandular organs 

 and the brain retain their weight and size. Indeed, the brain appears to 

 grow at about the normal rate to approximately the normal size under 

 these circumstances. 



Under the conditions described the body fat disappears in great meas- 

 ure through oxidation, and the proportion of the entire body substance 

 composed of water is markedly increased. The caloric value of a gram of 

 body tissues, sampled so as to represent the entire mass of tissues of an 

 animal which has undergone such a change, carried to the extreme limit, 

 may amount to only about one third of the normal value (Aron). 



When the control animals had trebled their original weight, Aron 

 fed certain of the stunted pups ad libitum, and found that while they were 

 able to round out their forms through fattening, and through enlargement 

 of the muscle fibers, they were unable to develop the normal form. Dur- 

 ing the period of stunting, the growth was largely due to changes in the 

 bones, and these, according to Aron, lose their capacity to grow as age ad- 

 vances, regardless of the size which the animal has attained. 



Aron deduced from such experimental evidence, that an infant which 

 does not increase in weight, or does so very slowly, is so. undernourished 

 that a portion of its body substance is being consumed. This would seem 

 to be too sweeping a conclusion. There are doubtless a number of con- 

 ditions under which an infant may not increase in weight, for a time, 

 when it is actually taking sufficient nutriment to support growth, provided 

 it were not handicapped by some factor aside from nutrition. It is, of 



