26 SECEETION. 



in the circulating fluid. 1 That urea is actually separated 

 from the blood by the kidneys is further confirmed by recent 

 observations, showing that in the renal artery the proportion 

 of this principle is about twice as great as in the renal vein. 3 



Adopting this view, we have nothing to do at present 

 with the formation of excrementitious principles. This takes 

 place in the tissues and is connected with the general process 

 of nutrition ; and in the excreting glands there is simply a 

 separation of matters already formed. The action of the ex- 

 creting organs being constant, there is not that regular peri- 

 odic increase in the activity of the circulation which is 

 observed in secreting organs ; but it has been observed that 

 the blood that comes from the kidneys is nearly as red as 

 arterial blood, showing that the quantity of blood which this 

 organ receives is greater than is required for mere nutrition, 

 the excess, as in the secreting organs, furnishing the water 

 and inorganic salts that are found in the urine. It has also 

 been shown that when the secretion of urine is interrupted, 

 the blood of the renal veins becomes dark like the blood in 

 the general venous system. 3 



The function of excretion is not, under all conditions, 

 confined to the ordinary excretory organs. When their func- 

 tion is disturbed, certain of the secreting glands, as the folli- 

 cles of the stomach and intestine, may for a time eliminate 

 excrementitious matters ; but this action is abnormal, and is 



1 In a recent work on the urine (ROBERTS, A Practical Treatise on Urinary 

 and Renal Diseases, Philadelphia, 1866, p. 359), it is stated on the authority 

 of observations and analyses by Oppler, Schottin, Perls, and Zalesky, that urea 

 and uric acid are actually produced in the kidneys. These statements, which 

 will be discussed more fully hereafter, are in direct opposition to facts that 

 have been regarded as settled by accurate analyses of the blood, and cannot 

 be accepted without confirmation. It is supposed, however, that urea and the 

 urates are the result of transformation of other excrementitious principles 

 existing in the blood, and are not formed de novo, like the elements of the true 

 secretions. 



2 ROBIN, Lecons sur les humeurs normales et morbides dw corps de rhomme^ 

 Paris, 1867, p. 89. 



3 BERNARD, Liquides de Torganisme, Paris, 1859, tome i., pp. 257 and 297. 



