208 THE PROTEIN ELEMENT IN NUTRITION 



investigations to determine the influence of a restricted diet on 

 growing dogs, Aron arrives at the following conclusions : 



A growing animal which receives only sufficient food to keep 

 its body weight constant, or to allow a slight increase, is in a 

 condition of severe starvation. 



If by a restriction of food the increase in weight is inhibited, 

 the skeleton grows at the expense of other parts of the body, 

 especially of the flesh. 



Most of the organs retain their weight and size, while the brain 

 grows to reach its normal weight. 



The composition of the body, when at a constant weight, 

 undergoes remarkable changes : fat is consumed more or less 

 entirely, the quantity of protein, especially of the muscles, but 

 not of the organs, is diminished, and a great proportion of the 

 body tissues is replaced by water ; thus this water and the 

 increase of the skeleton together replace the body material lost. 



The caloric value of 1 gramme body weight of an animal 

 which has undergone such a process to its extreme limit may 

 amount to only one-third of the normal value. 



It is possible by supplying suitable amounts of food to maintain 

 a dog in an emaciated condition, apparently in good health, and 

 at the weight of a puppy, for nearly one year, while its weight 

 at the end of the year should be three times as great. If such 

 an animal is thereupon fed amply, it fattens and rounds out, 

 but does not reach the size of a control animal which from the 

 beginning has been normally fed. It is unable to make good 

 the growth suspended by the long restriction of food. 



It will be readily recognized how very closely Aron's results 

 correspond to those obtained with dietaries poor in protein, as 

 exemplified by the rice-eating Bengali and Ooriya. Aron 

 experimented with dietaries deficient in energy and in all the 

 different elements. The Bengali and Ooriya show that very 

 similar effects are produced when the potential energy and 

 carbonaceous material of the diet being abundant the protein 

 element alone is deficient. 



THE INFLUENCE OF CERTAIN SUBSTANCES PRESENT IN THE FOOD 

 IN MINUTE QUANTITIES ON THE MAINTENANCE OF NUTRITION. 



Reference has already been made to the fact that recent lines 

 of research point to the presence of certain substances in the 

 food, present only in minute quantities, as being essential for 



