The Sweat Glands

A sweat-gland, like other glands, consists of a secreting portion and a conducting portion. The secreting portion is a long tubular alveolus coiled up in a knot and placed in the subcutaneous connective tissue at some distance from the epidermis. Generally the gland is formed of one such tubule only, but sometimes two tubules unite into a common duct. The duct beginning in the knot, in the convolutions of which it shares, runs a somewhat wavy but otherwise straight course verti­cally toward the surface of the skin onto which its lumen opens.

Through the epidermis the duct is nothing more than posed longitudinally or in an elongated spiral, and often a tubular passage excavated out of the epidermis with aremarkable corkscrew course, the turns of the screw becoming more open and the canal wider in the upper Dart as it approaches the surface. In the Malpighian layer the cells bordering on the passage are flattened and inclined downward so as to afford a more or less definite lining; there is a similar arrangement, but not so well seen, in the corneous layer. Reaching the dermis in a valley between papillae, the passage becomes a regular duct, with an independent epithelium of its own, a distinct basement membrane continuous with the upper surface of the dermis, and an outer coat of connective tissue strengthened, in the case of some of the larger glands, such as those of the axilla, with plain muscular fibres. The epithelium con­sists of two or three layers of small rounded cells, each with a relatively large but absolutely small nucleus, gene­rally staining deeply. The cells leave a narrow tubular thread-like lumen which is lined with a very characteristic distinct cuticle.

The duct continues to possess these characters after it has entered the knot and begun to pursue a twisted course, but soon changes suddenly into the secreting tubule. This may be distinguished from the duct by being wider, and by being lined by a single layer of cubical or columnar cells larger than those of the duct, bearing larger nuclei, andbehaving differently toward various staining reagents. The lumen though fairly distinct is not lined by any cuticle as in the duct. Lying between the basement membrane and the epithelial cells, or rather imbedded in the basement membrane, are seen a number of plain muscular fibres disposed longitudinally or in an elognated spiral, and often forming a distinct coat beneath the epithelium.

As in the case of other glands, we are unable to make any statement as to the work carried on by the epithelium lining the duct, but we may probably assume that the sweat is mainly secreted by the larger cells of the terminal coiled part of the tubule. These cells, therefore, like other secreting cells, are probably "loaded" and "discharged"; but as yet no structural changes in the cells corresponding to these phases have been satisfactorily ascertained, though after the administration of pilocarpine, which causes sweating, the cells of glands hardened in alcohol stain more deeply than usual with carmine. It must be remembered, however, that the sweat contains normally neither mucus nor proteid substances, and we should, therefore, not ex­pect to observe granules in the cells.

The peculiarly placed muscular fibres have been supposed, by their contraction, to assist in the flow of sweat along the tubule. In certain cutaneous glands of the frog, of a relatively simple nature, there is evidence that the secretion is ejected from the comparatively large lumen by the contraction of plain muscular fibres in the wall of the gland, or by a contraction of the wall itself, which is contractile without being distinctly differentiated into mus­cular tissue. And this rather supports the above view; but the matter is at present by no means clear.

The coil of a sweat gland is well supplied with bloodvessels in the form of capillary networks, and nerves have been traced to the tubes; but the exact manner in which these end is not as yet known.

Though present in all regions of the skin (of man), the sweat glands are unequally distributed, being more abundant in some regions, such as the palms of the hand, than in others. In the axilla are glands of very large size, and in these the ducts possess distinctly muscular coats.