THE GLANDS OF THE SKIN. 531 



The growth of the hair takes place by the constant formation by cellular 

 division of new cells, at first soft, upon the surface of the papilla, which represents 

 the matrix of the hair. These cells are situated upon the lower surface of the 

 hair-bulb, acquire the shape characteristic of the different portions of the hair to 

 which they become attached, and eventually undergo cornification. Thus, every 

 newly formed layer raises the hair to a higher level out of the follicle. Human 

 beings, between the eighteenth and twenty-sixth year, produce daily 0.20 gram of 

 hair-tissue corresponding to a loss of nitrogen represented by 0.0615 gram of 

 urea and even more in summer; and when frequently cut, according to Beneke, 

 14.6 grams of hair-tissue from the scalp annually. lodin or bromin, ingested 

 into the body, passes into the tissue of the hair. 



As to changes in ike hair, the statements made are by no means unanimous. 

 According to one view, after the hair has attained its typical length, the formative 

 process upon the surface of the hair-papilla is uninterrupted. The hair-bulb rises 

 from the papilla, becomes cornified, remains generally free from pigment, and is 

 finally raised more and more from the surface of the papilla, while its bulbous 

 lower extremity becomes fibrillated like a broom (Fig. 182). The lower portion 

 of the hair-follicle, thus made empty, diminishes in size; and upon the old papilla 

 a new hair is formed through resumption of the formative processes, while the 

 old soon becomes detached and falls out. In opposition to this view, Steinlein, 

 Stieda, and others, contend that the papilla of the old hair is destroyed, while a 

 new one forms in the hair-follicle, from whose surface the formation of the 

 new hair takes place. Finally, Kolliker and Waldeyer believe both that new hair 

 forms upon the old papilla and that its formation may take place upon a new 

 papilla. The statement that hairs may be newly formed in adults, as in the fetus, 

 is denied by v. Ebner. 



THE GLANDS OF THE SKIN. 



The sebaceous glands (Fig. 178, I, T) are simple acinous glands that in the 

 case of large hairs empty laterally by from one to three openings into the hair- 

 follicle, while in the case of small hairs the follicle projects free through the ex- 

 cretory duct of the gland (Fig. 183). The glands upon the labia minora, the 

 glans penis, the prepuce (Tyson's glands), and those upon the red surface of the 

 lips bear no relation to hair- follicles. The largest are present upon the nose and 

 the labia; they are entirely wanting upon the palm of the hand and the sole of 

 the foot. The glands contain polyhedral or circularly flat, nucleated, secre- 

 tory cells (Fig. 178, t), through whose proliferation several layers of epithelium 

 result, the elements of which undergo fatty degeneration as they advance toward 

 the lumen of the gland, where they are broken up into fatty detritus. The 

 membrane that gives form to the gland- vesicle is a structureless vitreous skin. 



The sudoriferous glands (Fig. 178, I, K), also designated sweat-glands, each 

 consist of a long, intestine-like, diverticular tube, whose extremity is rolled into a 

 convoluted mass in the subcutaneous connective tissue ; while the somewhat smaller 

 excretory extremity passes through the corium and the epidermis in a spiral 

 manner in the illustration it is shown in abbreviated form. The cells of the 

 sweat-glands are more compact, and are provided with intercellular and intra- 

 cellular secretory passages and a rod-shaped central body. The glands are 

 numerous and large on the palm of the hand, the plantar surface of the foot, 

 in the axilla, the groin, the forehead, and about the nipple; scanty on the dorsum 

 of the trunk; and are wanting on the glans penis, the prepuce, and the margin 

 of the lips. Modifications are seen in the glands about the anus, the wax-glands 

 of the ears (ceruminous glands), and the glands of Moll at the margin of the 

 lids (which empty into the hair-follicles of the eyelashes) . 



The glandular tube is lined within the convolution, in the smaller part of the 

 tube by a single layer of nucleated pavement-epithelium, and in the larger part 

 by cylindrical epithelial cells (Fig. 178, S) without membrane, and in part con- 

 taining fatty granules. The membrana propria is structureless and surrounded 

 by delicate connective-tissue fibrils. Unstriated muscular fibers pass in a longi- 

 tudinal direction on the larger glands (Fig. 178, S, a). The excretory duct 

 (sweat-canal) contains no muscular fibers and is lined by a laminated epithelium 

 of flat cells, whose surface possesses a thick, cuticular border. Within the epider- 

 mis, the canal pursues an intercellular course, without an independent mem- 

 brane, between the epidermal cells. A network of capillaries surrounds the con- 

 volution. Before the vessels become capillary, the arteries form an intricate net- 



