362 



LIQUID PARTS OF ANIMAL*. 



8. Urea. It has been long known that urea constitutes one 

 of the characteristic constituents of urine. Now urine is sepa- 

 rated from the blood by the kidneys, and it has been the general 

 opinion of physiologists, that the constituents of urine are not 

 merely separated from the blood by the kidneys, but that they 

 are actually generated from the blood by these organs. But 

 the experiments of Prevost and Dumas have demonstrated the 

 contrary of this. It follows from their experiments that urea 

 exists in blood ready formed ; but, as the kidneys are constantly 

 separating it from that liquid, the quantity of it, when the animal 

 is in a state of health, is always so small that it cannot be de- 

 tected in blood by the most delicate tests which we have it in our 

 power ta apply. Prevost and Dumas separated both the kid- 

 neys from dogs, cats, and rabbits, and examined the blood of 

 these animals four or five days after the excision. They always 

 discovered in this blood a notable quantity of urea.* As urea 

 exists in urine combined with lactic acid, there can be little 

 doubt that this is the case also with the urea in the blood. 



9. The preceding eight substances are the only ones (the salts 

 excepted) which have been hitherto shown to exist constantly in 

 healthy blood. A variety of other bodies have been noticed by 

 chemists, but they are omitted here, because their existence or 

 their characters have not been sufficiently constated. Thus Four- 

 croy and Vauquelin,-f- Proust,! and Orfila, announced the ex- 

 istence of bile in blood. Deyeux and Parmentier stated the ex- 

 istence of gelatin as a constant constituent of blood. || Deyeux 

 suggested the existence of a peculiar matter in the globules of 

 blood, to which he applied the name of tomellin, and to which he 

 ascribed the homogeneous concretion of the entire blood in the 

 preparation of puddings.! Denis makes osmazome one of the 

 constituents of blood.** All these and several other substances 

 noticed by Lecanu, as cruorin, erythrogen, have been omitted, be- 

 cause their existence in blood has not been demonstrated, nor 

 have their properties been sufficiently determined. 



10. Soda. -The serum of blood renders cudbear paper purple, 

 and therefore contains an alkali. This alkali in human blood is 



* Ann. de Chim. et de Phys. xxiii. 90. f Ibid. vi. 181, vii. 154. 



\ Ann. de Chim. xxxvi. 276. Elemens de Chiraie, ii. 313. 



|| Jour, de Phys. xliv. 438. 



1 Syst. de Conn. Chim. ix. 210. English translation. 



** Recherch. Experim, sur le Sang Hum. p. 107. 



