THE SKIN AND THE KIDNEYS 



197 



Experiment 63. Press the palm of the hand gently on a hand glass 

 or mirror. If convenient, have the surface of the glass cold. Repeat 

 the process with the back of the hand. Note any difference in the 

 relative amounts of perspiration. Try 

 these experiments on a very hot and a 

 very cold day, and note the difference 

 in the activity of the skin. 



265. Why we sweat. The most 

 important function of the sweat 

 is to regulate the temperature of 

 the body by evaporation from its 

 surface. We fan ourselves on a 

 hot day to hasten this evaporation 

 of the moisture on the skin. In 

 hot weather, and after taking a hot 

 drink or a hot-air bath, the skin 

 does its best to reduce the tem- 

 perature, and thus works all the 

 harder in pouring out the sweat 

 more profusely. When one is per- 

 spiring freely, it is highly impru- 

 dent to sit in a cool draught ; for 

 this evaporation may be suddenly 

 checked, and we are then apt to 

 take cold. 1 



but little, the cooling of the body is effected 

 chiefly by evaporation from the tongue, as 

 we see in the case of a panting dog. 



Profuse sweating is very common in 

 cases of debility and in excessively stout 

 persons. It occurs also in connection with 

 various diseases. Sudden emotion may 

 cause increased perspiration. 



1 Some people are afflicted with a natu- 

 rally strong and disagreeable odor of the 



FIG. 126. BLACKBOARD 

 SKETCH. 



Vertical Section of the Human 

 Skin. 



Magnified 30 diameters. 



Showing three outer layers of the 

 cuticle, two in black and a 

 middle light layer. Below the 

 inner dark layer, the active 

 layer (rete mucosuni) is well 

 shown. All below is the true 

 skin. The tortuous course of 

 a sweat gland is well marked. 

 The two round black spots are 

 fat cells. 



