1274 PHYSIOLOGY 



through the kidnpy- vessels. The flow through the vessels can be deter- 

 mined 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. 1119). 



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 hydrsemia, and especially 

 hydrsemic plethora caused by injection of normal saline into the circu- 

 lation, 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. 



Experiments on the action of diuretics have a close bearing on the 

 nature of the process occurring in the glomeruli. A large increase in 

 the urinary flow can be brought about by the intravenous injection 

 of saline diuretics such as sodium sulphate or potassium nitrate, or of 



