468 URO-GENITAL SYSTEM. 



ligature of the ureter, urea is found in much greater abun- 

 dance in the blood, and more rapidly induces urasmic poison- 

 ing. This question has been decided by the employment of 

 an incontestable means of estimating the amount of urea, viz. 

 by the process employed by Grehant : with Millon's reagent, 

 or the nitrous-nitrate of mercury, the urea is decomposed into 

 equal volumes of carbonic acid and nitrogen ; the especial 

 precision and characteristic feature of this process depends 

 upon the collection of all the carbonic acid and all the nitro- 

 gen, that is produced by this reaction, in such a manner 

 that in each analysis the equality of the determined volumes 

 of carbonic acid and nitrogen will render certain that only 

 urea has been decomposed. In this way it has been demon- 

 strated, that the accumulation of urea, after the operation of 

 nephrotomy, occurs in a continuous manner ; and that in this 

 case, as after ligation of the ureters, the quantity of urea 

 which accumulates in the blood is equal to the amount that 

 the kidneys would excrete ; that after ligation of the ureters, 

 the blood which leaves the kidney contains exactly the same 

 amount as that which enters this organ ; that in the normal 

 condition of the blood the renal vein contains less urea than 

 the renal artery, and that this deficit precisely corresponds 

 with the quantity of urea which is thrown off by the urine 1 

 during the same period of time. We have then the right to 

 conclude in an incontestable manner, that the kidney is 

 simply a filter, in which urea is eliminated, that is, the renal 

 filter can be impregnated with this substance and give it up 

 by drainage. 



B. Composition of urine. 



Urine is secreted during 24 hours in variable quantity, in 

 the normal condition to the amount of 500 to 1500 grammes. 

 This urine is an aqueous solution of various principles : its 

 elements in solution are pretty constant in quantity, the 

 variation being due to the proportion of water; in fact, 

 the urine is more or less abundant during health, because it 

 may be more or less diluted. 



The quantity of water in the urine depends upon the con- 

 ditions of the circulation and blood; as the urinary secretion 

 is a filtration resulting from pressure, when the arterial 



1 See Grehant, " Cours de PEcole Pratique de la Faculte de 

 Medecine de Paris." (" Revue des Cours Scientific nes." Nov.. 

 1871.) 



