EXCRETION. 



firmed in the human subject. In this case urea was found 

 to have accumulated in the blood as the consequence of an 

 injury received in the lumbar region. 1 



Since that time, as the processes for the determination 

 of urea in the animal fluids have been improved, this sub- 

 stance has been detected in minute quantity in the normal 

 blood by Marchand, a Picard, 3 Poisseuille and Gobley, 4 and 

 many others. Picard, indeed, carefully estimated and com- 

 pared the proportions of urea in the renal artery and the 

 renal vein, and found that the quantity in the blood was 

 diminished about one-half in its passage through the kid- 

 neys. 6 According to Robin, who apparently accepts the 

 results obtained by Picard, the blood in the renal vein con- 

 tains much less urea, urates, creatine, creatinine, chloride 

 of sodium, etc., than the blood of the renal artery. 6 Still 

 later urea has been found by Wurtz to exist in the lymph 

 and chyle in larger quantity even than in the blood. 7 



These facts, which have been almost universally regarded 

 as established, have led physiologists to adopt the view that 

 the peculiar excrementitious principles found in the urine 

 are not produced by the kidneys, but are formed in the sys- 

 tem by the general process of disassimilation, are taken up 

 from the tissues by the blood, either directly or through the 



1 SHEARMAN, Case of Mechanical Injury to the Kidneys, followed by Coma ; 

 Suppression of the Secretion of Urea by the Kidneys, and Absorption of the Urea 

 into the Blood- Recovery. The Monthly Journal of Medical Science, Edinburgh 

 and London, 1848, vol. viii. (New Series, vol. ii.), p. 666. 



2 MA.RCHAND, Sur la presence de Turee dans le sang. Annales des sciences natu- 

 relles, Paris, 1838, 2me serie, tome x., p. 46. 



3 PICARD, De la presence de Vuree dans le sang, These, Strasbourg, 1856. 



4 POISSEUILLE ET GOBLEY, Recherches sur Vuree. Comptes rendus, Paris, 1859, 

 tome xlix., p. 164, et seq. Poisseuille and Gobley found, as a rule, more urea 

 in the arterial than in the venous system. The blood from the carotid con- 

 tained 0*225 parts per 1000 ; that from the portal vein, 0'171 ; from the splenic 

 vein, 0*225, from the renal veins, 0'164 ; and from the femoral vein, 0'136. 



5 Op. cit., p. 38. 



6 ROBIN, Zecons sur les humeurs, Paris, 1867, p. 117. 



7 See vol. ii., Lymph and Chyle, pp. 520, 528. 



