92 VETEEINAEY HYGIENE 



show how entirely opposite the digestive apparatus is in the 

 two animals, and it gives us some insight into the process 

 of their nutrition. 



The object of food is to build up and repair the tissues, 

 and maintain a reserve for the body requirements ; these 

 requirements are energy and animal heat. Food as received 

 into the digestive tract is quite useless for the purpose of 

 the body; before it can be utilized it must form part 

 and parcel of the animal, either in the solid or fluid 

 tissues. 



Food by being absorbed and passing through the mem- 

 brane of the stomach and intestines into the general 

 circulation, practically becomes converted from dead into 

 living material ; this may not be literally trtie, but it makes 

 clear the fact that until the food supply finds its way into 

 the tissues of the body it is of no use. The digestive tract 

 from this point of view may be regarded as outside the 

 body. 



If the tissues of the animal be submitted to analysis, 

 they are found to group themselves under the following 

 heads : — 



(a) Nitrogenous tissues, containing carbon, hydrogen, 



oxygen, and nitrogen. 

 (h) Non - nitrogenous tissues, containing carbon, 



hydrogen, and oxygen, nitrogen being absent. 

 (c) Mineral matters, 

 (rf) Water. 



The proportion of these existing in an animal must 

 necessarily vary with the condition, or even from day to 

 day ; still it is remarkable how closely the proportions are 

 maintained, even in animals of different classes. 



In the following table* the animals were in a half fat 

 condition, and the percentage proportion of the constituents 

 of the body are calculated after deducting the contents of 

 the stomach and intestines. 



Lawes and Gilbert. 



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