THE SWEAT-GLANDS. 



443 



blind tube, whose lower end is arranged in the form of a coil placed in the areolar tissue under 

 the skin, while the somewhat smaller upper end or excretory portion winds in a vertical, 

 slightly wave-like manner, through the chorium, and in a cork-screw or spiral manner through 

 the epidermis, where it opens with a free, somewhat tvumpet-shaped, mouth. The glands are 

 very numerous and large in the palm of the hand, sole of the foot, axilla, forehead, and around 

 the nipple ; few on the back of the trunk, and are absent on the glans. prepuce, and margin of 

 the lips. The circumanal glands and the ceruminous glands of the external auditory meatus, 

 and Moll's glands, which open into the hair-follicles of the eyelashes, are modifications of the 

 sweat-glands. 



Each gland-tube consists of a basement membrane lined by cells ; the excretory part or 

 sweat-canal of the tube is lined by several layers of cubical cells, whose surface is covered by a 

 delicate cuticular layer, a small central lumen being 

 left. Within the coil the structure is different. The 

 first part of the coil resembles the above, but as the 

 coil is the true secretory part of the gland, its structure 

 differs from the sweat-canal. This, the so-called distal 

 portion of the tube, is lined by a single layer of moder- 

 ately tall clear nucleated cylindrical epithelium (fig. 

 294, S), often containing oil-globules. Smooth muscu- 

 lar fibres are arranged longitudinally along the tube in 

 the large glands (fig. 294, S, a). There is a distinct 

 lumen present in the tube. As the duct passes through 

 the epidermis, it winds its way between the epidermal 

 cells without any independent membrane lining it 

 (Reynold). A network of capillaries surrounds the 

 coil. Before the arteries split up into capillaries, they 

 form a true rete mirabile around the coil (Brilcke). This 

 is comparable to the glomerulus of the kidney, which 

 may also be regarded as a rete mirabile. Numerous 

 nerves pass to form a plexus, and terminate in the 

 glands (Tomsa). 



The total number of sweat-glands is estimated by 

 Krause at 1\ millions, which gives a secretory surface 

 of nearly 1800 square metres. These glands secrete 

 sweat. Nevertheless, an oily or fatty substance is often 

 mixed with the sweat. In some animals (glands in 

 the sole of the foot of the dog, and in birds) this oily 

 secretion is very marked. 



Numerous lymphatics occur in the cutis, some arise 

 by a blind end, and others from loops within the papilla 

 on a plane lower than the vascular capillary. [These 

 open into more or less horizontal networks of tubular 

 lymphatics in the cutis, and these again into the wide 

 lymphatics of the subcutaneous tissue, which are well 

 provided with valves.] Special lymphatic spaces are 

 disposed in relation with the hair-follicles and their 

 glands (Neumann), [and also with the fat (Klein). The 

 lymphatics of the skin are readily injected with Berlin 

 blue by the puncture method]. 



The blood-vessels of the skin are arranged in several systems. There is a superficial system, 

 from which proceed the capillaries for the papilla?. There is a deeper system of vessels which 

 supplies special blood-vessels to (a) the fatty tissue ; (b) the hair-follicles, each of which has a 

 special vascular arrangement of its own, and in connection with this each sebaceous gland 

 receives a special artery ; (c) an artery goes also to each coil of a sweat-gland, where it forms a 

 dense plexus of capillaries (Tomsa). 



285. THE SKIN AS A PROTECTIVE COVERING. The subcutaneous 



fatty tissue fills up the depressions between adjoining parts of the body and covers 

 projecting parts, so that a more rounded appearance of the body is thereby ob- 

 tained. It also acts as a soft elastic pad and protects delicate parts from external 

 pressure (sole of the foot, palm of the hand), and it often surrounds and protects 

 blood-vessels, nerves, &c. It is a bad conductor of heat, and thus acts as one of 

 the factors regulating the radiation of heat ( 214, II., 4), and, therefore, the 

 temperature of the body. The epidermis and cutis vera also act in the same manner 

 ( 212). Klug found that the heat-conduction is less through the skin and sub- 



Fig. 299. 



Sebaceous gland, with a lanugo hair, a, 

 granular epithelium ; b, rete Malpighii 

 continuous with a ; c, fatty cells and 

 free fat ; d, acini ; e, hair-follicle, with 

 a small hair, /. 



