230 REPORTS ON INVESTIGATIONS AND PROJECTS. 



tinue the experimental feeding long enough to obtain answers to many ques- 

 tions concerning the chemistry of nutrition. Since nearly all our animals 

 are still in fine health and apparently normal condition after several months 

 of experimental feeding with the food mixtures containing protein-free 

 milk, it seems probable that such experiments can be continued throughout 

 the greater part of the natural life of the animal, and thus afford an 

 opportunity to study many of the more intricate problems of physiological 

 chemistry. 



The experiments just mentioned concern only the maintenance of mature 

 animals. More important and interesting, however, are the results of our 

 experiments in feeding young and growing animals. When young rats are 

 fed with mixtures of isolated food substances, such as were used with a 

 considerable degree of success during the first year's work, they can be 

 maintained in apparent health and activity for many months, but make little 

 or no growth. Measurements of several rats thus stunted, which have 

 kindly been made for us by Drs. Donaldson and Hatai, have shown that in 

 respect to the proportion of all their parts these stunted rats had remained 

 of the same size as at the beginning of the experiment. The only evidence 

 of development was shown by the water content of their brains, which was 

 normal for their age. Thus, while their brains had not increased in size, 

 their brain tissue had matured. 



The outcome of these experiments is interesting in connection with the 

 attempts of other investigators to retard the growth of animals by supply- 

 ing an insufficient quantity of normal food. In such cases, while the animals 

 remained stationary in weight their skeletons and nervous systems developed 

 at the expense of their muscular tissue. 



When young rats are fed on mixtures containing protein-free milk and 

 one or another of the pure proteins, they make normal growth on all of the 

 proteins thus far tried with the exception of those soluble in alcohol, which 

 are obtained from the seeds of the cereals. When the food mixtures con- 

 tain only these latter proteins (we have thus far used gliadin from wheat 

 and hordein from barley), the experimental animals have been kept in excel- 

 lent nutritive condition throughout periods which have now reached nearly 

 one year and give promise of continuing successfully much longer. Sev- 

 eral animals have thus been fed from the time of weaning until they should 

 have attained almost their maximum size, but without making more than the 

 slightest growth. Many experiments are now in progress to determine the 

 effect of such arrested growth on the subsequent development of the animals, 

 but as yet the experiments have not been continued long enough to furnish 

 data suitable for publication. 



The results of these investigations conducted during the past two years 

 have been summarized in the publications of the Carnegie Institution of 

 Washington, Publication No. 156, just issued, and in Publication No. 156, 

 part 2, now in press. 



