66 



PER SP IRA TION. 



peculiar liquids which they pass out through tubes. 

 Such organs are called glands : the liquid which a gland 

 collects or manufactures, is known as its secretion; and 

 the tube through which the secretion is poured is named 

 a duct. Two kinds of glands empty their 

 secretion on the skin. They are the 

 sweat, or sudoriparous, glands, and the oil, 

 or sebaceous, glands. 



13. The Sweat-Glands (Fig. 23) make 

 the perspiration. They are very slender 

 tubes which reach from the surface, 

 through epidermis and dermis, to the 

 fatty tissue beneath the skin. There the 

 tube coils up into a knot. These glands 

 are found all over the skin, but not 

 equally distributed. In the palm of the 

 hand there are nearly three thousand to 

 each square inch: on the middle of the 

 back, where they are fewest, about four 

 hundred in the same space. There are 

 in all about two and a half millions of 

 sweat-glands. 



14. The Perspiration or Sweat is a 

 transparent colorless liquid, consisting 



mainly of water. Anything tending to heat the body 

 causes perspiration to flow more freely, so its amount 

 is very variable. On an average, it is at least two pounds 

 daily. The sweat may dry up, or evaporate, as fast as it 



13. Describe a sweat-gland. What is the number of these glands 

 in a square inch of the palm ? Of the skin of the back? How many 

 are there altogether in the skin ? 



14. Describe the sweat. Why is it variable in amount? What is 

 its average quantity ? What is " insensible" perspiration ? Sensible ? 



FIG. 23 A sweat- 

 gland. , horny lay- 

 er of the cuticle; c, 

 deeper layer of the 

 cuticle; 6, the der- 

 mis. The duct of the 

 gland is seen to run 

 through the epider- 

 mis and dermis and 

 end in a coiled mass 

 placed in the fatty 

 tissue beneath the 

 skin. 



