EXCRETORY SYSTEM 361 



Sweat glands. If the outer surface of the skin is 

 examined with a hand lens, many minute pores, or 

 openings, will be seen. These are the openings of the 

 sweat glands which lie embedded in the lower part of 

 the dermis. Around each sweat gland is a network of 

 blood vessels. As the blood flows through these capil- 

 laries, the glands take from it a fluid from which they 

 produce sweat or perspiration. This is over 99% water, 

 dissolved in which are some salts and nitrogenous waste. 

 Perspiration is an excretion, but its chief function, as 

 we shall see later, is to regulate the temperature of the 

 body. 



The hair. The hair is an outgrowth from the epi- 

 dermis. Each hair is situated in a tube-like sac called 

 the follicle, formed by the epidermis dipping down into 

 the dermis. At the bottom of the follicle is a little 

 bulb made of capillaries and nerves. It is from this 

 bulb that the hair grows in length, and from this a 

 new hair grows to replace an old one. A hair is a 

 slender tube of hard dry cells, the interior of which is 

 filled with cells containing coloring matter. Opening 

 into the hair follicle are the ducts from the oil glands. 

 The secretion from these glands keeps the skin moist 

 and also makes the hair soft and more pliable. The 

 glands may be made more active by massaging and 

 vigorous brushing. If the hair is kept properly oiled, 

 it does not become so brittle, and consequently is less 

 liable to break or to split. 



The condition of the hair depends upon the healthful- 



