CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 723 



shew, as we have said, that these multiply by division ; we have no 

 evidence of multiplication taking place elsewhere in the epidermis. 

 The more superficial cells of the Malpighian layer, thrust upwards 

 by the new comers, are transformed into the cells of the stratum 

 granulosum ; and although we do not as yet fully understand the 

 exact nature of the transformation we may conclude that the 

 peculiar granules of these cells are concerned in the manufacture 

 of keratin. Changed by the consumption of their granules in this 

 manufacture the cells of the stratum granulosum become first the 

 cells of the stratum lucidum and then the cells of the distinctly 

 horny layer, pushed upwards through which by the new formations 

 continually succeeding below them, they pass to the surface and 

 are eventually shed. 



436. 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 towards the surface of the skin on to which its lumen 

 opens. 



Through the epidermis the duct is nothing more than a 

 tubular passage excavated out of the epidermis with a remarkable 

 corkscrew course, the turns of the screw becoming more open and 

 the canal wider in the upper part as it approaches the surface. 

 In the Malpighian layer the cells bordering on the passage are 

 flattened and inclined downwards 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 papillaB, 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 distin- 

 guished 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, and behaving differently towards 

 various staining reagents. The lumen though fairly distinct is 



