238 STUDIES IN PHYSIOLOGY 



involuntary muscle run out toward the outer regions of the 

 skin (Fig. 111). When these muscles contract, hairs are 

 made to assume an erect position, or in other words to 

 " stand on end." In the skin of a cat the muscles attached 

 to the base of the hairs are specially developed. 



Glands of the Skin. Two kinds of glands are found in the 

 skin, namely, the oil or se-ba'ceous (Latin, sebum = grease) 

 and the sweat or per-spi'ra-to-ry glands. The former are 

 found in most parts of the skin, being most numerous in 

 the scalp and in the skin of the face. Like hairs, however, 

 they are wanting on the palms of the hands and the soles of 

 the feet. Sweat glands, on the other hand, are most numer- 

 ous in the regions just named. One writer estimates that 

 there are 2800 sweat pores on every square inch of the sur- 

 face of the palm, and that the total number of these glands 

 in one's skin is about 2,500,000. 



Sebaceous Glands. In form these glands resemble small 

 irregular sacs (see Fig. 111). The mouths of the sacs 

 open most frequently into the cavity of a hair follicle. 

 The cells in the interior of the gland are formed into a kind 

 of oily secretion which keeps the hair from becoming dry 

 and brittle. This liquid also spreads more or less over the 

 surface of the skin and makes it oily and less permeable 

 to water. At the edges of the eyelids the sebaceous 

 glands are especially large and their secretion prevents the 

 lids from sticking together. 



Perspiratory Glands. We have already called attention 

 to the pores that may be seen on the surface of the epider- 

 mis of the hand. From one of these openings one can trace 

 in a section of the skin a more or less spiral duct inward 

 through the epidermis and the dermis, until in the fatty 

 layer below the skin the little tube coils itself into a knot 

 (see Fig. 111). In this inner region a fine capillary network 

 runs about the cells of the gland. Here the blood and lymph 

 Jose a considerable amount of water, together with a small 

 amount of urea and salts. These ingredients make up the 



