THE KIDNEYS AND THE URINE. 79 



What is the daily quantity of urine secreted ? 



One to two quarts. The quantity varies greatly in health with 

 the amount of fluid taken, of food consumed, of the activity of the 

 skin evaporation, and somewhat with the character of the food. In 

 a more general way it may be said to depend upon the condition of 

 the blood, an excess of fluids demanding increase of functional ac- 

 tivity on the part of the kidneys. In conditions of disease or under 

 the stimulus of drugs the limits mentioned are by no means final, 

 for in certain pathological conditions the secretion may be almost 

 wholly suspended or very greatly increased. 



What conditions increase the urinary secretion? 



The conditions which favor filtration of water by the glomeruli 

 of Malpighi ; that is, the presentation of a larger amount of blood 

 to the action of these bodies. This is accomplished 



(1) By increasing the force of the heart. 



(2) Through the nervous system by its action upon the vascular, 

 so as to produce local congestion. The effect of the nervous sys- 

 tem in increasing the urine by reflex vaso-motor impulses is felt 

 most in the glomeruli, and the urine is therefore very watery. 



(3) Conditions which cause anaemia of other parts may produce 

 a greater determination of blood to the kidneys, and so increase 

 the urinary flow. So marked is this that the skin and kidneys 

 may almost be said to be complementary in their action in elimi- 

 nating water from the system ; and in this regard their relative 

 activity may be said to be inversely proportional to one another. 



Kirke has the following table (modified from Foster), which is 

 useful for reference : 



Table of the Relation of the Secretion of Urine to Arterial Pressure 



(Kirhe}. 



A. Secretion of urine may be increased 



a. By increasing the general blood-pressure by 



1. Increase of the force or frequency of heart-beat. 



2. Constriction of the small arteries of areas other than that 



of the kidney. 



b. By increasing the local blood-pressure by relaxation of the renal 



artery, without compensating relaxation elsewhere by 



1. Division of the renal nerves (causing polyuria). 



2. Division of the renal nerves and stimulation of the cord, 



below the medulla (causing greater polyuria). 



