THE PERSPIRATION. 791 



phates. The fat is either derived from the fatty matter of the plasma 

 of the blood, or more probably from the metamorphosis of the albu- 

 minoid contents of the epidermic cells of the sebaceous glands. ^ It 

 is poured out, partly on the surface of the skin, but more commonly 

 into the interior of the hair follicles, or even into the most minute 

 ones. It contributes to soften and render flexible both the hairs and 

 the skin, and, by protecting the latter from the action of water or 

 aqueous solutions, it renders the skin more effectual as a defensive 

 organ. The so-called ceruminous and Meibomian glands of the ear 

 and eyelids, may be regarded as special modifications of sebaceous 

 follicles. 



In all Quadrupeds which .possess hairs, sebaceous or oil glands exist ; the 

 glandulce Uropyyii, or caudal glands, of Birds, supplying the fatty secretion 

 with which they anoint their feathers, are highly developed sebaceous glands. 



The epidermic tissues generally, viz., the cuticle, nails, and hairs, 

 have been viewed as solid excreted substances. When worn, cut, shed, 

 or desquamated, they undoubtedly rid the economy of a large amount 

 of nitrogenous, sulphurous, and ferruginous matter. The continual 

 loosening of epithelial cells from the gastro-pulmonary cavities, must 

 serve a similar office. 



The sudoriferous, sudoriparous, or sweat glands, are present, in 

 larger or smaller numbers, in all parts of the skin. They are small, 

 rounded, pinkish bodies, placed immediately beneath the true skin, 

 and average about Jth of a line in diameter. Each sweat gland consists 

 of a fine tube, closed and coiled up into a ball at its deeper end, from 

 which a straight part of the tube, or duct, passes up through the cutis 

 and cuticle, and opens by a somewhat widened orifice on the surface. 

 When the cuticle is thick, as in the palms and soles, this tube passes 

 through it in a spiral manner (Fig. 66, 5, 6). The whole tube, when 

 unrolled, measures about Jth of an inch in length, and about 5 JQ of an 

 inch in width. This tube consists of an outer vascular coat, prolonged 

 from the cutis, and of an epidermoid lining, continuous with the cu- 

 ticle ; the spiral portion is composed of the latter only. Two coiled 

 tubes may unite into one duct. When a sweat gland is destroyed, it 

 is not reproduced. In some situations the sweat glands are of large 

 size, as in the axillae, where they measure nearly two lines in diameter, 

 are of a darker red color, are composed of branched tubes, and secrete 

 a thick, exceedingly acrid, and odorous fluid. In the palms and soles, 

 the openings of the sweat glands, the so-called pores of the skin, are 

 found on the papillary ridges ; in other parts, they are scattered over 

 the surface. They are most numerous on the palm of the hand, where 

 2800 orifices are found on a square inch ; they are fewest on the back 

 of the neck and trunk. Non-striated muscular fibres, arranged longi- 

 tudinally, exist in the vascular coat of the ducts of the larger sweat 

 glands. (Kolliker.) 



The perspiration, or sweat, which is excreted by the sudoriferous or 

 sudatory glands, is not the only watery exhalation from the skin ; for 

 water is undoubtedly exhaled from the integument generally, as well 



