176 EXCEETION. 



from the excretions. It was noted by Erichsen, 1 in his case 

 of extroversion of the bladder, and it has been further shown 

 by experiments upon dogs, that there is an alternation of 

 action upon the two sides. Bernard exposed the ureters in 

 a living animal and fixed a small silver tube in each, so that 

 the secretion of both kidneys could be readily observed ; and 

 he noted that a large quantity of fluid was discharged from 

 one side for from fifteen to thirty minutes, while the flow 

 from the other side was slight and in some instances was 

 entirely arrested. The flow then commenced with activity 

 upon the other side, while the discharge from the opposite 

 ureter was diminished or arrested. 2 We are already familiar 

 with this mode of action in the parotid glands. 3 



Changes in the Composition of the Blood in passing 

 through the Kidneys. Some of the changes in the blood in 

 its passage through the kidneys have already been noted. 

 The most important of these consist in a diminution in the 

 proportion of urea, the urates, and other of the excrementi- 

 tious principles found in the urine. This would be expected, 

 inasmuch as these principles are constantly present in the 

 urine, and have been shown to be derived exclusively from 

 the blood. It has been ascertained, also, that the blood of 

 the renal veins contains less water than the blood of any 

 other part of the venous system. 4 The constant separation 

 of water from the blood by the kidneys, for the purpose of 

 carrying off the soluble excrementitious principles, is an ex- 

 planation of this fact. It was also observed by Simon, a 

 number of years ago, that the blood of the renal veins does 



1 ERICHSEN, loc. tit, p. 361. In this case, the openings of both ureters 

 were exposed to view, and Erichsen states that " the two ureters do not open 

 at the same time, but with an irregularly alternating action." 



2 BERNARD, Unpublished lectures delivered at the College of France in the 

 Summer of 1861. During the progress of this course of lectures, we had an 

 opportunity of observing the alternate action of the two kidneys, 



3 See vol. ii., Digestion, p. 160. 



4 ROBIN, Lefons sur les humeurs, Paris, 1867, p. 80. 



