CHAP, vi.] OF DIS-ASSIMILATION AMONGST ANIMALS. 137 



in a liquid form, through the respiratory organs as vapour. Let 

 us note, by the way, that this pulmonary vapour is charged with 

 putrescible, azotized particles. 



But water, in its liquid state, is not excreted alone ; it carries 

 with it a quantity of mineral substances, mostly saline, some 

 acid. The salts in solution in the water are carbonates, sul- 

 phates, phosphates, etc., certain of which have only traversed 

 the organism to leave it as they entered it; some of them, 

 however, are directly formed in the organism. Carbonic acid, 

 for example, so abundant in living solids and liquids, can unite 

 with the bases which it meets there. On the other hand, it is 

 probable that the combustion of proteic matters in nutrition 

 leads to the formation of 'sulphuric and phosphoric acids, which, 

 on their side, also combine with the bases, either directly, or 

 by displacing weaker acids. It is certain, in fact, that these 

 salts always come together in the ashes of protei'c matters 

 directly burned. Finally, it has been proved that all prolonged 

 intellectual labour in man corresponds to an abundant excretion 

 of phosphates through the kidneys, and it is known that the 

 nervose tissue is very rich in phosphorus. 1 



To the mineral acids must be added organic acids ; some, not 

 azotized, such as the lactic acid (C 6 H 5 5 ,HO) probably result 

 from the oxydation or evolvement of the hydrocarburets of the 

 fats ; others are azotized, and proceed from the oxydation of 

 protei'c matters. These acids, which have a fixed formula, like 

 mineral acids, are only formed in the tissues of animals, and 

 once constituted, they act exactly like the ordinary mineral acids, 

 and unite with the bases to form salts, which are also expulsed 

 by the ordinary ways. The principal of these azotized organic 

 acids are uric acid (C 40 H 4 Az 4 O 6 ) very abundant in man, the car- 

 nivorous mammifers, birds and reptiles ; and hippuric acid (C 18 H 8 

 O 8 Az,HO), which is met with most in the herbivorous mammifers. 



1 Byasson, Essai sur le Rapport qui Existe, d, lEtat Physioloyique, entre 

 VActiviti Cbrtbrale et la Composition des Urines. (Theses de la Faculte de 

 Medecine de Paris, 1868, n 162.) 



