218 JMANUAL OF CATTLE-FEEDIKG, 



Presupposing the existence of a liealtliy and well-developed 

 organibHi, we may specify four conditions as, from our 

 point of view, the mobt important : 



1. The facts of common experience appear to show un- 

 mistakably that a liberal supply of protein in the food is 

 one of the conditions of any sustained muscular exertion. 

 Working animals must receive not only an abundance of 

 food, but of food rich in protein, and the more severe the 

 work, the more concentrated must be the food ; and the 

 same fact is equally true of the human animal. This, 

 however, does not necessitate the conclusion that the pro- 

 tein is the source of the power exerted : its decomposition, 

 as we have seen, goes on independently of muscular exer- 

 tion, and may be regarded as simply one of the conditions 

 of the healthy activity of the muscles or of their normal 

 nutrition. 



2. The largely increased excretion of carbonic acid and 

 water during work indicates a necessity for a liberal supply 

 also of the non-nitrogenous constituents of food. At need, 

 however, this demand may be supplied by the albuminoids 

 or perhaps by fat already formed in the body. 



3. An essential condition of continued activity of the 

 muscles is the constant removal from them by the circula- 

 tion of the carbonic acid and other chemical products 

 formed duiing contraction. Certain of these products, 

 notably lactic acid and acid potassium phosphate, if allowed \ 

 to accxunulate in the muscle, produce the sensation of 

 weariness and shortly incapacitate it for further action. If 

 they be removed, either by the blood or by injection of a 

 weak salt solution, the muscle is again capable of work ; 

 while, if they be injected into a fresh muscle, they produce 

 the same effect as if naturally formed there. The same 

 accumulation of waste products goes on in the muscle after 



