EXPERIMENTAL OBSERVATIONS 387 



kidney, but no proven secretory influence has been shown. The variations 

 in the secretion of urine that follow nervous stimulation are quite satisfactorily 

 explained by the changes in the blood flow. 



The kidney can be placed in an onkometer and its variation in volume 

 measured directly, figures 301 and 302. This volume measurement, when 

 taken with the arterial pressure, gives a very good index of the volume of 

 blood flowing through the kidney. Now when the kidney is inserted in an 

 onkometer and the urine collected from the ureter, it is found in general that 

 the greater the pressure and flow of blood the greater the secretion of urine, 

 as would follow if the glomerulus were a filtering mechanism. However, if 

 the renal vein is partially obstructed, even though the blood pressure be in- 

 creased, the amount of urine secreted is sharply decreased. If the vein is 



FIG. 301. Diagram of Roy's Onkometer. a Represents the kidney enclosed in a metal box, 

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

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

 and inside metal capsules (the latter not represented in the figure), the two being firmly screwed 

 together by screws at h, and on the opposite side. 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 *'. After the kidney has been enclosed in the capsule, the mem- 

 branous 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 Onkograph, figure 302. 



completely occluded, the secretion of urine not only ceases for the time but 

 does not immediately begin again when the blood pressure and flow are re- 

 established. The closure of the vein for only one or two minutes is said to 

 stop the flow of urine for as much as forty-five minutes. This short inter- 

 ruption of the circulation is sufficient to bring about other changes in the 

 glomerular epithelium, for it now excretes albumin, which it did not previously 

 let pass. Therefore, it is not pressure merely that favors the secretion, but 

 there must be an efficient flow of blood. The secretion is influenced espe- 

 cially by the amount of blood flowing through the kidney in a given time. 



