Human Physiology. 215 



pouring out the matter of perspiration separated from the blood. 

 A square inch of the human skin contains 3,500 pores. Each 

 pore is the mouth of a long twisted tube, a sort of drain pipe a 

 quarter of an inch long, ending in a gland which secretes from 

 the blood the matter of perspiration. These tubes are said to 

 be in the aggregate forty miles long. Commonly the matter 

 passes out in a state of vapour, or is immediately dissolved in 

 the atmosphere. It is then called insensible perspiration. But 

 let the circulation be quickened, and the action of the skin 

 increased by exercise, or simply by a high temperature, and the 

 fluid is poured out so fast as to gather in great drops over the 

 whole surface of the body. 



Take a single sweat gland more highly magnified, and we 

 shall get a good idea of its structure. There it is (Fig. 56), a 

 tube divided into a loop, and the loop rolled up into a ball. 

 This is surrounded by a net-work of capillaries and nerves. 

 When the nerves have the energy of health, they somehow 

 compel the blood to part with that portion of its matter which 

 it can best spare. They drain off the matter the system wishes 

 to be rid of. If you have been drinking beer or brandy, it 

 will pass into these glands by some force of attraction, and 

 pass off at the pores ; or eating onions, or herrings, or smoking 

 tobacco. The clothing is soon tainted and made foul with the 

 matter of perspiration. 



In Fig. 57 a magnified section of skin shows a sweat gland 

 and its tube, and also the roots of two hairs, which are also 

 furnished with glands giving out an oily matter. 



As some substances excite the action of the intestinal glands, 

 others stimulate the action of the sweat glands, and excite to 

 profuse perspiration. It would seem that in all these cases 

 matter is taken into the body which it wishes to be rid of; 

 and some kinds find one outlet and some another. The skin 

 will absorb some things which pass out by the lungs or kid- 

 neys. Dip a finger in spirits of turpentine, and in a few 



