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PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



Distinctive Uses of the Kinds.— The albuminoids 

 are used mainly for tissue-building, and they alone can 

 be used for this purpose, for the tissues are themselves 

 albuminoid. But whatever of albuminoids is left over 

 from tissue-building is used for fuel also — i. e., for force 

 and heat making. The amyloids and fats can be used 

 only for force and heat, for these do not contain the 

 nitrogen necessary for the formation of tissue. Thus 

 an animal fed on amyloids and fats alone can not con- 

 tinue to live indefinitely for want of the necessary repair 

 of the tissues. This is called nitrogen starvation. There- 

 fore tissue-making can be done only by albuminoids, 

 but force and heat making by all three kinds. 



Illustrations. — Carnivores fed on lean meats con- 

 sume only albuminoids. They use first whatever is 

 necessary for repair of tissues, and whatever is left 

 over is burned for force and heat. Herbivores take 

 albuminoids in, relatively, small quantity; their food is 

 mostly amyloids. They probably use the whole of their 

 albuminoids for repair, and their amyloids for force and 

 heat. Man is an omnivore, but, except the livers on rice 

 or potatoes, he probably takes more albuminoid than 

 is necessary for repair. What is left over, which we 

 shall call albuminoid excess, he uses for force and heat. 

 All the amyloids and fats are used for the latter 

 purpose. 



Waste Tissue. — But the waste is not wasted. This 

 also is burned as fuel. But since in the adult the waste 

 is exactly equal to the repair, it is evident that the 

 equivalent of the whole* albuminoid food is burned as 

 fuel for force. But since amyloid and fats are also 

 burned, it is evident that the equivalent of the whole 

 food is burned for force and heat. 



* Except an incombustible part, as explained hereafter. 



