268 REPORTS ON INVESTIGATIONS AND PROJECTS. 



ever, with the exception of casein, yield all of the amino-acids known to be 

 decomposition products of the so-called complete proteins. None of the 

 proteins which do not yield all these amino-acids, except glycocoll, promote 

 growth, e. g., gliadin, hordein, zein, or gelatin. 



Not all of the so-called complete proteins promote growth, e. g., conglutin, 

 legumin, vignin, or phaseolin. Why these leguminous proteins fail has not 

 been discovered. 



Young rats which from the time of weaning make a normal rate of 

 growth on the above diets fail to continue to grow after attaining from 75 

 to 80 per cent of the maximum weight normal for mature animals. After 

 remaining at a constant weight for some weeks these animals decline, and 

 soon die, unless a change is made in the diet. If supplied with a food con- 

 taining whole milk powder they rapidly regain their lost weight but can not 

 then again grow normally on the original experimental diet. Our experi- 

 mental foods seem to lack some ingredient present in milk which is essential 

 at some stage of their early growth. 



Rats which fail to grow on a diet containing an inefficient protein, like 

 gliadin, live longer than those which grow on a diet containing an efficient 

 protein. The failure of the latter appears to be due to the absence of some- 

 thing in the food essential for the development of some organ which develops 

 during growth. 



An artificial mixture of inorganic ions, lactose, and citric acid, in imitation 

 of the "natural protein-free milk" has, in some cases, proved as effective in 

 promoting growth as the natural product. The majority of the experiments 

 have, however, thus far led to a less rapid growth, and for a shorter time. 



Experiments with the "artificial protein-free milk" have shown that growth 

 to nearly full adult size can be obtained with a diet which contains only pure 

 protein, starch, lactose, inorganic ions, and citric acid. This diet was en- 

 tirely free from fat and all substances soluble in ether, and was chemically 

 the simplest food on which an animal has yet been made to grow in any 

 degree corresponding to the normal. 



Experiments with the "artificial protein-free milk" have also shown that 

 the chemical constitution of the carbohydrate of the food has a great influ- 

 ence on growth. No growth has been made on any diet in which lactose was 

 replaced by sucrose or any other sugar. 



Rats can be kept at perfectly constant weight for many months by feeding 

 with a diet containing "artificial protein-free milk" and gliadin, and an ideal 

 method is thus provided for studying the effect of arrested development. 



The addition of a small amount of an adequate protein to a diet contain- 

 ing a protein on which no growth can be made, leads at once to a normal 

 rate of growth. 



The combination of gliadin and gelatin, on neither of which alone can 

 growth be made, leads to a very considerable growth. 



A certain minimal quantity of protein is necessary for growth. Above 

 this amount growth is proportional to the amount of protein until an opti- 



