NUTRITION AND GROWTH: I, 37 



animal which to a certain extent oppose each other, the tendency to grow 

 and the tendency to maintain life. (Erhaltungstrieb.) 



In the first periods of the experiments it appears that the tendency to 

 grow in a young animal is greater than the tendency to maintain life. 

 The further course of the experiments shows that the tendency to maintain 

 life finally secures the upper hand. Therefore, the tendency to maintain 

 life appears to be the greater biologic power. This observation is fully in 

 accord with the results of investigations by Moreschi." This author, at 

 the suggestion of Ehrlich, studied the influence of a restriction of food on 

 tumors in mice. He found that by a suitable restriction of food the 

 growth of a tumor could be suppressed, that the tendency of the tumor 

 to grow is not greater than the tendency to maintain life in the animal. 

 Of course, this may depend on the malignancy of the tumor; in his ex- 

 periments the power of the tumor-cells to attract material of nutrition 

 was not greater than that of the normal tissue-cells. 



We find similar conditions in our experiments : While the bones 

 attract food material with great power, in order to grow, this tendency 

 is finally overcome by that of the animal to maintain its life. 



Some observations made by Waters and mentioned above, which lead 

 to very similar conclusions, may be quoted here. 



This author says that "ungrown animals that had been previously well 

 nourished continued to increase in height and in width of hip for a considerable 

 length of time, even though on a starving ration. Apparently, the animal organ- 

 ism is capable of drawing upon its reserve for the purposes of sustaining the 

 growth process for a considerable time and to a considerable extent. Our ex- 

 periments indicate that after the reserve is draAvn upon to a certain extent to 

 support growth, the process ceases and there is no further increase in height or 

 in length of bone. From this point on, the animal's chief business seems to be 

 to sustain life. This law applies to animals on a stationary live weight as well 

 as to those being fed so that the live weight is steadily declining, and, indeed, 

 to those whose ration, while above maintenance, and causing a gain in live 

 weight, is less than the normal growth rate of the individual. Such an animal 

 will, while gaining in weight, get thinner, because it is drawing upon its reserve 

 to supplement the ration in its effort to grow at a normal rate." 



We see from om- experiments that the skeleton of all parts of the 

 body has the strongest "tendency to grow." While the other portions 

 not only do not increase, but lose constantly during the time when the 

 animal maintains itself by burning its fat and muscle tissue, the bones 

 increase in weight and size. Indeed, we find the paradox that while 

 protein in the muscles diminishes in quantity, that of the bones increases. 

 The brain, from what ^ye hino seen, alpo seems to have an intensive 

 tendency to grow. The other internal organs also have doubtless a 

 sufficient tendency, at least to maintain themselves. The muscles suffer 

 a greater reduction than any other part of the body, and seem to have 



^'' Ztschr. f. Immunitatsforsch. u. exp. Ther. (1909), 2, 651. 



