FUNCTIONS OF THE NUTRIENTS 193 



masses of eggs from the body substance, and it seems 

 unlikely that so much nuclein as is needed exists in the 

 flesh. If a cow gives thirty poimds of milk daily, nearly 

 or quite a pound of casein must come from somewhere, 

 and there is no evidence that any ordinary ration would 

 contain so large a quantity of phospho-proteins of like 

 constitution. Hens' eggs are rich in nuclein, beyond any 

 amount which the food seems likely to supply. Experi- 

 mental evidence supports these general inferences. 



278. The function of certain unidentified bodies. — 

 An important addition to the science of nutrition is the 

 recent demonstration that certain compounds are asso- 

 ciated with animal foods which have a growth-promoting 

 function and in the absence of which either artificial or 

 natural foods fail to sustain growth and even life. (See 

 Par. 118.) It has been known for some time that some 

 such substance was associated with the shells of rice which, 

 when given to animals afflicted with beri-beri from eating 

 polished rice, woidd restore them to a normal condition. 

 Substances of this class were named vitamines by Funk. 



An enlargement of the knowledge of bodies of this 

 class was led up to through studies by American 

 investigators as to the relative nutritive value of single 

 proteins. Heretofore the attention of investigators in 

 animal nutrition has been focussed chiefly upon the con- 

 structive and energy functions of the various classes of 

 nutrients, and it was expected that when the proteins, 

 carbohydrates, and ash compounds, supposedly necessary 

 to complete nutrition, were all supplied to an animal, 

 satisfactory results would be accomplished. It was dis- 

 covered that, when there was fed a combination of puri- 

 fied nutrients artificially prepared with great care and in 

 accordance with the best knowledge of the needs of the 



