FUNCTIONS OF THE SKIN. 157 



called sensible perspiration when it accumulates enough to 

 be perceptible. 



The amount of perspiration is about one quart in twenty- 

 four hours. 



The amount varies with : 



1. Temperature, dryness, and rate of renewal of air. 



2. Condition of the blood ; e.g., if watery from drinking 

 much water. 



3. Muscular exercise. 



4. Certain drugs some exciting perspiration ; e.g., cam- 

 phor : others diminishing it ; e.g., belladonna. 



5. The nerves exercise great influence on the activity of 

 the cells of the gland. 



The Functions of the Skin. 1. Protective, (a) As a 

 tough covering, (b) As aided by the oil from the oil glands. 



2. Excretory, (a) Giving off sweat. (V) Also a little 

 carbon dioxid. 



3. Absorptive, (a) Oxygen, to a slight amount, may be 

 taken, (&) and medicine (rubbing in ointments). 



4. Sensory organ of touch. 



5. Heat-regulating. 



Next to its excretion, the heat-regulation by the skin is the 

 most important for our present consideration. 



Regulation of the Temperature of the Body by the 

 Skin. It is a striking fact that, except in disease, the tem- 

 perature of the body varies only a little from 98.5 F. in sum- 

 mer and winter, during exercise and rest. The rate of heat- 

 production varies greatly. The rate of giving off heat must 

 therefore vary accordingly. Otherwise the temperature of the 

 body would soon reach the boiling-point (in thirty-six hours) ; 

 and, as the body is largely composed of water, it would be 

 cooked, and part of it disappear as invisible gas. But long 

 before reaching 212 F. the tissues would be killed. 



