CHAP, nr.] OF ANIMAL NUTRITION. 123 



having oxydized them, urea, urates, creatine, creatinine, inosie 

 acid, inosates, and so on. 



A very general fact, and one which it is very important to 

 point out, is that all truly animal organisms cannot live without 

 constantly absorbing complex organic substances, and that they are 

 powerless to create these themselves, at least in sufficient quantity, 

 from the mineral world, whence it is necessary that they should 

 draw a supply, either from other animals or from vegetals. 



The blood of the superior animals is the great mart in which 

 the anatomical elements provide themselves with the substances 

 which are necessary to them, and reject those which encumber 

 them. As a consequence of its office in the vital movement, the 

 blood is itself necessarily subject to a perpetual exchange of 

 materials. It gives to, and takes from, the anatomical elements 

 on the one hand, and on the other, to and from the ambient 

 medium. It borrows oxygen from the outer air by means of 

 the respiratory organs ; it receives from the digestive organs 

 immediate principles, restorative nutriments liquefied or dissolved. 

 Finally, the totality of the lymph, when it exists, continually 

 diffuses itself in the blood. On the other hand, the tissues 

 yield to it the dissolved or liquid residues of vital combustion. 



The expenditure of the blood balances its acquisitions. It 

 exhales, by means of the lungs and skin, water, carbonic acid, 

 and azote ; it expels through diverse special channels, water 

 and complex organic substances. Of the latter the most part 

 are purely regressive, and destined to be returned to the 

 mineral kingdom; the others are modified by special secreting 

 organs, and become fit to play a more or less important part in 

 the various physiological functions. Finally, on the other hand, 

 the blood yields to the anatomical elements the three orders 

 of immediate principles indispensable to their conservation, the 

 oxygen which burns and vivifies them, the water which soaks 

 them, diverse mineral salts, hydro-carbonic ternary substances, 

 new prote'ic matters which, in each anatomical element, replace, 

 molecule by molecule, the exhausted materials. 



