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TEXT-BOOK OF PHYSIOLOGY 



and is composed of large nucleated cells, the lowest layer of which, the 

 " prickle cells," contains the pigment granules which give to the skin 

 its varying hues in different individuals and in different^races of men; 

 the corneous layer is composed of flattened cells which from their 

 exposure to the atmosphere, etc., are hard and horny in texture. 



The Sweat-glands. These glands are tubular in shape, the inner 

 extremity of each being coiled upon itself a number of times, forming 



a little ball situated 

 in the derma or 

 the subcutaneous 

 connective tissue. 

 From this coil the 

 duct passes up in a 

 straight direction to 

 the epidermis, 

 where it makes a 

 few spiral turns, 

 after which it opens 

 obliquely on the 

 surface. The gland 

 consists of a base- 

 ment membrane 

 lined with epithelial 

 cells. It is sup- 

 plied abundantly 

 with blood-vessels 

 and nerves. The 

 sweat - glands are 

 extremely numer- 

 ous all over the 

 cutaneous surface, 

 though they are 

 more thickly dis- 

 posed in some situ- 

 ations than others. 

 They p rob ably 

 average 2500 to the 



square inch; the total number has been estimated at from 2,000,000 

 to 2,500,000. 



Influence of the Nerve System on the Production of 

 7 T?^ secretion of sweat, though a product of the activitv 

 I epithelial cells and dependent on a variety of conditions, is reg- 

 ulated to a large extent by the nerve system. Here as in other 

 secreting glands the fluid is derived from materials in the lymph- 

 spaces, furnished by the blood. Generally the two conditions, in- 



FIG. 199. SECTION PERPENDICULARLY THROUGH THE 

 HEALTHY SKIN. a. Epidermis, or scarfskin. 6. 

 Rete mucosum, or rete malpighii. c. Papillary 

 layer, d. Derma, corium, or true skin. e. Pan- 

 niculus adiposus, or fatty tissue. /, g, h. Sweat- 

 gland and duct, i, k. Hair, with its follicle and 

 papilla. /. Sebaceous gland. 



