NUTRITION AND GROWTH: I. 3 



different individuals of the same species and especially in different 

 species of animals. The rabbit and the dog have an upper limit which 

 is very high, that is, these animals have a great "tendency to grow," 

 while the human has only a small one. 



The process of growth depends, not only upon this "tendency to 

 grow," but also on the food. The "tendency to grow" induces the 

 normal production of new tissues only when the material necessary for 

 the construction of these new tissues is furnished by the food. The 

 quantity of growth, to the upper limit of this tendency, is determined 

 by the food. Eubner expresses the same idea when he says that "nutri- 

 tion has a moderating influence on the process of growth." Therefore, 

 the rate of growth depends upon two factors, the "tendency to grow" 

 and the nutriment. Eapid growth takes place if this tendency is 

 high in the cells and a sufficient quantity of food is taken to furnish all ■ 

 the substances needed. If there is no such tendency, then even the 

 maximum intake of food will not lead to gTowth. It would naturally 

 be expected that the converse should also be true; in spite of a high 

 "tendency to grow" no growth should take place if the substances 

 needed for this growth are not present in the food. 



We must apply the laws of energy in studying the influence of nourish- 

 ment on growth. From this point of view a growing animal requires 

 food for two purposes: first, like the adult, to replace the energy ex- 

 pended in the production of heat and the work of the vegetative organs; 

 and, second, for the formation of new body substances. This division 

 of the needs of a growing animal into (1) energy required for main- 

 tenance and (2) energy required for growth, seems to be logical and it 

 is adopted by the most competent authors dealing with this subject.* 



The intake of energy, in order to enable an organism to grow, must 

 exceed thd requirement for maintenance, and this excess of energy is 

 used for the formation of new body substances. However, in this 

 instance it is not simply a question of energy in the form of calories; 

 the protein intake also must exceed the demand for wear and tear and 

 the excess of protein is stored in the form of new body cells. Similar 

 considerations apply to certain inorganic constituents of food. Since 

 the excess over the requirement for maintenance alone will be used 

 in the formation of new body substances, the amount of growth will 

 depend on the amount of this excess. 



A further deduction leads to the conclusion that no growth will take 

 place if there is in the food no excess over the amount of energy required 

 for maintenance. In other words, it should be possible, by a proper 

 restriction of the food, to suppress all growth. This conclusion has been 

 accepted frequently without question. Gerhartz,^ for example, regarded 



* Ostertag und Zuntz, Landtoirtsch. Jahrb. (1908), 37, 211. 

 "Biochem. Ztschr. (1908), 12, 97-118. 



