170 EXCRETION. 



suppose that these principles are produced in the various 

 tissues and organs of the body during the process of disassim- 

 ilation,'are taken up by the blood, and are simply separated 

 from the blood by the kidneys. There may be unimportant 

 modifications of some of these principles in the kidneys 

 or in the urine, such as the conversion of a certain amount 

 of creatine into creatinine, but the great mass of excremen- 

 titious matter is separated from the blood by the kidneys 

 unchanged. 



Extirpation of one kidney from a living animal is not 

 necessarily fatal. "We have frequently performed this opera- 

 tion as a class-demonstration, and kept the animal for weeks 

 and months, without observing any indications of disturbance 

 in the eliminative functions. If the operation be carefully 

 performed, the wound will generally heal without any diffi- 

 culty, and in most instances the remaining kidney seems 

 sufficient for the elimination of urine for an indefinite period. 

 In all of our experiments, save one, the animals, killed long 

 after the wound had healed, never presented any marked 

 symptoms of the retention of excrementitious matters in 

 the blood. It is a noticeable fact, however, that in many 

 instances they showed a marked change in disposition, and 

 the appetite became voracious and unnatural. These ani- 

 mals would sometimes eat faeces, the flesh of dogs, etc., 

 and, in short, presented certain of the phenomena so fre- 

 quently observed after extirpation of the spleen. 



In no instance have we been able to observe enlargement 

 of the remaining kidney, even many months after the extirpa- 

 tion of one of these organs. In one experiment, of which a 

 record of the facts was made at the time, a dog, from which 

 one kidney had been removed, was kept for one year and 

 nine months and then killed while in perfect health. The 

 remaining kidney presented no abnormal characters, and was 

 of the same size as the other, which had been preserved in 

 alcohol. There appears to be a general but rather indefinite 



