1915] Casimir F-unk 345 



greater in quantity in the case of butter, was very effective. This 

 fact strengthens my belief that the stimulating action of butter-fat 

 may be due to vitamine. It is regrettable that Osborne and Mendel 

 did not determine whether the oily f raction contained nitrogen. 



On summarizing this section we see that the growth-promoting 

 substance was found only in materials from sources which are 

 known to contain vitamines, e. g., milk, cod-liver oil, beef-fat, etc. 



Question of thermo-stability of the growth-promoting sub- 

 stance. Here we also find great divergence of opinion as in the 

 case of beriberi-vitamine. Thus, Hart and Lessing (50) observed 

 complete arrest of growth in young rats fed on sterilized milk. On 

 the other band McCollum and Davis (124) were able to obtain an 

 active extract from boiled eggs. They went even further: butter- 

 fat was hydrolyzed (131) in petroleum ether, at room temperature, 

 with an alcoholic potassium hydroxid Solution. After neutraliza- 

 tion the soaps were extracted with olive-oil and the growth-promot- 

 ing factor was found intact. Osborne and Mendel (136) also con- 

 sider the growth-promoting substance thermo-stable. 



Role of amino-acids in growth. This problem was studied 



extensively by Osborne and Mendel, and by McCollum. The former 



authors usually arranged their experiments as they did those men- 



tioned above. In the artificial diet, containing butter-fat and protein- 



free milk, the casein was replaced by protein known to be deficient 



or poor in certain amino-acids. It was found by Osborne and 



Mendel (138) that gliadin without addition of lysin was inadequate 



for growth. The same applies to zein without addition of trypto- 



phan. In another paper (139) they. stated that the addition of 



cystin and lysin made an inadequate supply of casein suitable for 



growth. Lactalbumin was found to promote growth very strik- 



ingly. This protein was found to yield more tryptophan than that 



from any other protein and they attribute the influence on growth to 



the presence of this amino-acid. In this inference there is the fal- 



lacy, however, that lactalbumin may contain vitamine from milk. 



These authors found, also, that a deficiency in any particular in- 



gredient of the diet did not induce a corresponding compensatory 



increase in the food intake (140)- 



McCollum (141) found that the proteins of milk are superlor to 



