NITROGENOUS METABOLISM 155 



of the diet, but, in great part, that ordinarily furnished by 

 protein food. 



From all this it appears that much of the protein which 

 we eat serves only to supply the tissues with carbohydrate. 

 The impression is likely to be that this is a roundabout 

 and not an economical way to provide sugar, which might 

 have been taken as such at the outset. The facts may 

 fairly be employed to support the modern teaching that 

 excess of protein is to be avoided, but we have already 

 shown the necessity for allowing more than is actually to 

 be reconstructed after the digestive dismembering. Recog- 

 nizing as inevitable the discarding of amino-acids, we can 

 see the desirability of having them made to furnish a 

 simple standard food like sugar, valuable for its store of 

 energy. The possibility of glycogen formation from pro- 

 tein naturally follows. The glycogen of carnivorous 

 animals presumably has such an origin. The maintenance 

 of the sugar of the blood during long fasting is also ascribed 

 to the disintegrating protein of the tissues. Given dex- 

 trose in such quantities, the production of fat from protein 

 becomes at least theoretically possible. Broadly speaking, 

 we may claim for protein that it can do all that any form 

 of organic food can do for the system. Yet this does not 

 impair the statement, equally to be recognized, that car- 

 bohydrates and fats should form much the larger part of 

 the income. 



After the constructive requirement has been met, all ad- 

 ditional protein seems to entail unprofitable labor on the 

 part of the liver in deaminizing the cleavage products, the 

 presence of various substances of a possibly detrimental 

 nature in the circulation, and an activity on the part of the 

 kidneys which may amount to an abuse of these important 

 excretory organs. There is this general contrast between 

 the behavior of proteins and non-proteins in the body: 

 the former give rise to rather complex waste-products im- 

 posing a task upon the liver and kidneys; the latter are 

 oxidized cleanly to carbon dioxid and water, two com- 

 pounds which are eliminated with ease. A fuller discus- 



