EXCRETION. 483 



passed, but in a different way, viz., by constricting the arteries generally, 

 and, among others, the renal arteries; the diminution of blood-pressure 

 resulting from the local resistance in the renal arteries being more 

 potent to diminish blood-pressure in the glomeruli than the general 

 increase of blood-pressure is to increase it. Section of the renal nerves 

 which produces local dilatation without greatly diminishing the general 

 blood-pressure will cause an increase in the quantity of fluid passed. 



(3) The fact that in summer or in hot weather the urine is dimin- 

 ished may be attributed partly to the copious elimination of water by 

 the skin in the form of sweat which occurs in summer, as contrasted 

 with the greatly diminished functional activity of the skin in winter, 



Fig. 307. Diagram of Roy's Oncometer. a, represents the kidney inclosed in a metal box, 

 which opens by hinge/; b, the renal vessels and duct. Surrounding the kidney are two chambers 

 formed by membranes, the edges of which are firmly fixed by being clamped between the outside 

 metal capsule, and one (not represented in the figure) inside, the two being firmly screwed together 

 by screws at 7i, and below. The membranous chamber below is filled with a varying amount of 

 warm oil, according to the size of the kidney experimented with, through the opening then closed 

 with the plug i. After the kidney has been inclosed in the capsule, the membranous chamber above 

 is filled with warm oil through the tube e, which is then closed by a tap (not represented in the 

 diagram); the tube d communicates with a recording apparatus, and any alteration in the volume 

 of the kidney is communicated by the oil in the tube to the chamber d of the Oncograph, fig. 295. 



but also to the dilated condition of the vessels of the skin causing a 

 decrease in the general blood-pressure. Thus we see that in regard to 

 the elimination of water from the system, the skin and kidneys perform 

 similar functions, and are capable to some extent of acting vicariously, 

 one for the other. Their relative activities are inversely proportional 

 to each other. 



The intimate connection which exists between the volume of the kidney 

 and the variations of blood -pressure is exceedingly well shown with the 

 Oncometer, introduced by Roy, which is a modification of the plethysmo- 

 graph, fig. 307. By means of this apparatus any alteration in the volume of 

 the kidney is communicated to an apparatus [oncograph], capable of recording 

 graphically, with a writing lever, such variations. 



