PERSPIRATORY GLANDS. 413 



Regulation of Temperature. When the temperature of 

 the muscles is raised to 49 C. they lose their contractility. This 

 figure has been regarded as the highest that can be reached by a 

 living human being ; indeed, much below this, 45 C., has long 

 been considered as fatal, although a temperature of nearly 52 C. 

 has been recorded. When the temperature falls to 19 C. a fatal 

 result will follow. 



To prevent the body from becoming too hot is one of the 

 functions of the skin. This it accomplishes by radiation, con- 

 duction, and evaporation. Of the total heat given off from the 

 body, 73 per cent, is by radiation and conduction from the skin, 

 and 14.5 per cent, is by evaporation. Thus there is carried off by 

 the skin nearly 88 per cent, of the total heat. This topic will again 

 be discussed in the consideration of the skin and its functions. 



The prevention of the reduction of the temperature of the 

 body to an extent that would be harmful is accomplished by wear- 

 ing proper clothing, by the ingestion of food, both solid and 

 liquid, by warming the air which comes in contact with the body, 

 and by increased muscular activity. The use of alcohol for this 

 purpose is, as previously stated, delusive. 



THE SKIN. 



The skin is composed of a deep portion, the corium, derma, or 

 true skin ; and of a superficial portion, the epidermis or cuticle. 



Corium. The corium makes up by far the greater part of 

 the skin, and within it are the perspiratory glands, the sebaceous 

 glands, the hairs, together with both blood- and lymphatic vessels. 

 The upper surface, where it joins the epidermis, is irregular, 

 being composed of elevations papillae and intervening depres- 

 sions. In some of these papillae are the tactile corpuscles, in which 

 nerve-fibers end. 



Epidermis. The epidermis is made up of a deep and a 

 superficial layer. The deep layer (rete mucosum or rete Malpighii) 

 covers the papillae of the corium and fills the depressions between 

 them. It is composed of cells, round or of different shapes due to 

 pressure of contiguous cells, the material of which they are com- 

 posed yielding readily. It is in this layer that the pigment is 

 deposited which characterizes the dark races. The superficial 

 layer of the epidermis is composed of cells which are flat and 

 dry or horny. 



Perspiratory Glands. The perspiratory glands, also de- 

 scribed as sweat- and sudoriparous glands, are very numerous, it 

 being estimated that in the entire skin there are not less than 

 2,400,000. They are more abundant in some parts of the body 

 than in others : in the palm of the hand there are 42 to the square 

 centimeter; on the forehead, 190; and on the cheek, 85. If all 



