166 SKIN AND KIDNEYS. 



warm weather, and when exercising actively, we perspire 

 freely, and the amount of urine is reduced; when we exer- 

 cise less, and especially in cold weather, we perspire less, 

 and the urine is more abundant. Cold drives the blood from 

 the surface. Consequently more blood goes to the kidneys 

 (as well as to the other internal organs), and they throw off 

 much more water, though probably little if any more urea. 

 The average daily amount of urine is about three pints. The 

 quantity is increased by high blood pressure, copious drinking, 

 by cold air (driving the blood from the skin), nitrogenous 

 food, certain drugs, etc. It is diminished by a lowered blood 

 pressure, profuse sweating, diarrhea, non-nitrogenous food, 

 some diseases of the kidneys, etc. 



The blood leaving the kidney, especially when in full 

 activity, is still bright red ; it is probably the purest blood in 

 the body. 



What is the effect of all the processes thus far studied on 

 the weight of the body ? 



READING. The Skin and its Troubles, D. Appleton & Co. 



