THE SKIN. 51 



gofng on, and while the evaporation is equal to the amount of 

 fluid poured out the sweat is not seen. This is called insen- 

 sible perspiration. When the body becomes heated, and the 

 sweat increases so as to form in drops, it is known as sensible 

 perspiration. Under certain nervous influences the skin be- 

 comes bathed in sweat, as in the cold sweat of fear. The 

 quantity of sweat poured out varies with the season. In 

 hot weather it is much more profuse than in cold. Violent 

 exercise increases the flow, so also will too much clothing. 

 Sudden changes in the weather, or in the amount of clothing, 

 or sitting in a draught after being heated, are very apt to 

 arrest evaporation and cause a chilliness of the body, followed 

 by a "cold" or by "congestion of the lungs." 



Perspiration is a colorless fluid, consisting mostly of water. 

 It has a peculiar odor, more marked in some persons than in 

 others, and moro in some races of people than in others. 

 There is also solid matter in sweat. Salt can be detected 

 by tasting it. The worn-out tissues of the body and of the 

 skin are found in it; but these vary very much, according 

 to the attention paid to the skin. 



5. The Oil Glands. Besides the sweat glands, there are 

 also oil glands in the skin. These are little sacs found in 

 connection with the hairs, and clustering around them, some- 

 times in pairs, but often as many as from four to eight to 

 one hair. Each little sac communicates with the hair by a 

 duct, along which the oil flows to the root of the hair, and 

 then finds its way out to the surface of the skin. It is 

 nature's dressing for keeping the hair from becoming crisp 

 and brittle, and for keeping the skin soft and moist. 



These glands are more numerous on the face and where the 

 hair is thick. They are not usually found where there is no 

 hair, as on the palm of the hand. It often happens that 

 some of these glands get blocked up, forming unsightly little 



