572 



THE URINARY APPARATUS 



[CH. XXXYI1I. 



each heart-beat, and larger waves, which accompany respiration. In 

 some cases larger sweeping waves (Mayer curves) are seen as well, 



FIG. 37(3. Oncometers for 



but they are absent in the tracing reproduced : if, in such a 

 tracing, the kidney curve is compared with the tracing of arterial 



FIG. 377.- -Curve taken by renal oncometer compared with that of ordinary blood-pressure, cr, Blood- 

 pressure curve ; b, kidney curve. (Roy.) 



pressure, it will be seen that the rise of pressure is simultaneous with 

 the fall in kidney volume due to constriction of the renal vessels. 



The Functions of the Kidney. 



The function of the kidneys is to separate the urinary con- 

 stituents from the blood, and by this means the blood is maintained 

 of constant composition. The kidrfey cells are remarkably sensitive, 

 so that alterations in the composition of the Blood which are too 

 slight to be detected by chemical analysis (such as an increase of 

 water or of chlorides after a meal) are felt by the kidney, and 

 increased secretion (diuresis) occurs. In the case of some urinary 

 constituents, they are practically entirely removed by the kidney ; 

 urea is an example of this class. In other cases excess beyond a 



