408 MANUAL OF PHYSIOLOGY. 



The following are the more important points in the argu- 

 ment: 



1. The blood does normally contain most of the important sub- 

 stances found in the urine ; so they need not necessarily be made 

 in the kidney. 



2. The blood in the vessel leading to the kidney the renal 

 artery is said to contain more urea than the vessel leading from 

 it the renal vein so that the blood appears to lose urea in pass- 

 ing through the kidney. 



3. If the ureters be tied, and the elimination be thus prevented, 

 urea accumulates in the blood. This can hardly be made by the 

 kidney, because 



4. If the renal arteries be tied so that no blood goes to the 

 kidneys to effect the elaboration of urea in those organs, then 

 the same accumulation results, showing that the kidneys are cer- 

 tainly not the only organs where urea is made. 



5. Extirpation of the kidneys also gives rise to a great increase 

 of the urea in the blood. The amount of urea in the blood 

 after nephrotoiny is said to increase steadily with the time which 

 elapses after the operation, and the amount accumulated corre- 

 sponds to the amount that would have been normally excreted in 

 the same time, had the animal not been operated upon. 



6. Lastly. In some diseases which greatly interfere with or 

 quite suppress the secretion of the kidneys, an accumulation in 

 the blood of certain poisonous or injurious materials takes place, 

 and gives rise to the gravest symptoms called ursemic poisoning, 

 which closely coincide with those observed in experimental anni- 

 hilation of the renal function. 



From the foregoing it would appear to be satisfactorily settled 

 that the urea, which is by far the most important ingredient of 

 the secretion of the kidney, is probably made elsewhere and not 

 in that organ, whose duty seems to be chiefly to remove it from 

 the blood. This is most probably also true of all the other organic 

 constituents of the urine. The question then arises : Where is the 

 urea formed ? 



We naturally turn for an answer to the most widespread and 

 most actively changing nitrogenous tissue, namely, muscle. Here, 



