142 PHYSIOLOGY. 



secretion into a cavity where it might accumulate, instead 

 of evaporating as fast as it is poured out. Of course the 

 kidneys have a somewhat different work from the skin, 

 but in its general plan of working we might say they 

 are skin turned outside in. The kidney unit (the tubular 

 gland) has branches ; i.e. is compound. The kidney is a 

 compound gland of excretion, internal in position. Both 

 skin and kidneys excrete a large amount of water, with 

 salt and some other matter in common. 



Relation between the Work of the Kidneys and that 

 of Skin. There is a very immediate relation between 

 the work of the kidneys and that of the skin. In warm 

 weather, and when exercising actively, we perspire freely, 

 and the amount of urine is reduced ; when we exercise 

 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 dimin- 

 ished by a lowered blood pressure, profuse sweating, 

 diarrhea, non-nitrogenous food, and some diseases of the 

 kidneys, etc. 



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. 



Summary. i. The skin throws off sweat, which is water contain- 

 ing waste matter. . 



