1190 



PHYSIOLOGY 



blood pressure or to a constriction of the renal blood vessels. By taking 

 these two records it is possible to tell whether a given increase of blood flow 

 through the organ is of local or of general causation, i. e. is active or passive. 

 Thus the volume of the kidney gives us an indirect clue to the pressure in 

 and the flow through the kidney vessels. The flow through the vessels 

 can be determined directly either by a cannula in the inferior vena cava, all 

 veins other than the renal being clamped, or by Brodie's method, already 

 described (p. 1037). 



The results of the experiments carried out by these methods can be 

 represented in the following tabular form : 



It will be seen that in every case, where an increased blood flow attended 

 with a rise of blood pressure in the glomerular capillaries is brought about, 

 the urinary flow is at the same time increased. 



Another factor, altering the ease with which filtration of watery fluid 

 and salts would take place through the glomerular capillaries, would be the 

 composition of the blood plasma. Any dilution of this plasma must render 

 filtration more easy, while a concentration would make it more difficult. 

 As a matter of fact hydreemia, and especially hydraemic plethora caused by 

 injection of normal saline into the circulation, evoke an increased flow of 

 urine. A smaller effect is produced by injection of defibrinated blood, and 

 if the blood has been previously concentrated by depriving the animals of 

 water, there may be little or no increase in flow, in consequence of the high 

 osmotic pressure of the proteins of the plasma injected. 



If the glomerular function is that of mere filtration, we should expect 

 that the more rapidly the process occurs, the more nearly would the urine 

 which is turned out into the ureters resemble the blood plasma in com- 

 position, reaction, and osmotic pressure, since the glomerular filtrate hurried 

 through the tubules would have very little time to undergo any changes 

 resulting in its concentration. If, on the other hand, the diuresis produced 

 by salt or sugar solutions is to be ascribed to a stimulation of the renal 



