FOOD OF ANIMALS. 193 



I have now given the uses of the different constituents of the 

 blood. The red disks carry oxygen to the interior of the tissues 

 and thus lead to their decomposition, and carry off a portion of 

 the products of their decomposition, the carbonic acid ; the nitro- 

 genized products being carried off by the kidneys in the shape of 

 urea and lithic acid. The fibrin is the plastic matter out of which 

 the tissues are formed. T-^ proportion as it is consumed it is re- 

 placed by the albumen, v^^^ich in the colorless cells, is converted 

 into fibrin. The loi> ; of tne albumen is itself supplied by the 

 food. II, 



We are now prepai/; 1 for examining into the nature of the 

 food of animals. , ,, 



, One great object of food is t,,, s'upply the blood with a portion 

 of albumen, to replace tl^at whiu^ disappears by its conversion in- 

 to fibrin and finally into organized tissue. Since animals are inca- 

 pable of forming proximate princo^esfrom their elements, the food 

 must contain albumen ready formed. 



The simplest form of nutrition is that presented by carnivorous 

 animals, and I therefore begin with it as it takes place in them. 



Living on the flesh of animals of the same composition as 

 their own, they simply dissolve this flesh in their digestive canal 

 and convert it into an albuminous solution. The earthy matters 

 contained in bones, being insoluble in the gastric juice pass 

 along the intestinal canal and are rejected as foeces, which in these 

 animals consist almost exclusively of the earthy portion of bones 

 with hairs and other insoluble matters. 



The albuminous solution resulting from the digestion of the 

 flesh is absorbed by the lacteal vessels, and enters the mass of the 

 blood, to replace the albumen which has been converted into fibrin, 

 and finally expended in the nutritive process. 



A portion of the tissues is then decomposed and ultimately re- 

 jected from the system, in form of carbonic acid and urine ; a cor- 

 responding amount of matter is withdrawn from the blood to form 

 new organized tissue, and a corresponding amount of nutritive 

 matter is introduced into the blood to compensate for this loss. 



We ought then, to find in the excretions of the animal, the same 

 amount of matter and the same elements differently combined, as in 

 the food ; not that the food is directly converted into these excre- 

 tions, for it has first to pass through the state of organized 



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