206 NORMAL HISTOLOGY. 



of a substance, called "eleidin," within the cytoplasm (Fig. 183). 

 These cells form the "stratum granulosum." The eleidin appears 

 to be produced at the expense of the cytoplasm, the process being 

 a form of degeneration, so that after a while the whole cell is con- 

 verted into a homogeneous material in which the nucleus persists 

 in a form deprived of chromatin, and therefore insusceptible of 

 staining. The presence of these cells gives rise to the formation of 

 the "stratum lucidum " immediately above the stratum granulosum. 

 Within this stratum the eleidin appears to pass into a closely related 

 substance of a horny nature, keratin, and the cells become con- 



Fig. 183. 



Cell from the stratum granulosum of the epidermis of the scalp. (Rabl.) The cytoplasm of 

 the cell has been in great measure converted into granules of eleidin ; the chromatin of 

 the nucleus has retracted into a compact mass in the centre of the nuclear region, and is 

 destined to disappear. This cell is from a section made parallel to the surface of the 

 epidermis, which accounts for its shape and apparent size. 



verted into firmly compacted scales, which make up the most super- 

 ficial or horny layer of the epidermis. 



The sweat-glands are simple tubular glands, the deep ends of 

 which are irregularly coiled to form a globular mass situated in 

 the deeper portion of the corium or at various depths in the sub- 

 cutaneous tissue. From these coils the excretory duct passes 

 through the corium to the epidermis, where it opens into a spiral 

 channel between the epidermal cells, ending in an orifice at the sur- 

 face of the skin. 



The epithelial lining of the sweat-gland is a continuation of the 

 stratum mucosum, from which it is derived, and consists of two or 

 more layers of cubical cells in the duct and of a single layer of more 

 columnar cells in the deeper, secreting portion of the gland. In 

 the duct these cells rest upon a homogeneous basement-membrane, 

 but in the secreting portion there is a more or less complete layer 

 of elongated cells, similar in appearance to those of smooth muscular 

 tissue, which lie between the epithelial cells and the basement-mem- 

 brane (Fig. 184). It is doubtful whether these are really muscle- 

 cells. The loops of the glandular coil are surrounded by fibrous 

 tissue, which contains the bloodvessels supplied to the gland and 

 serves to support it in its globular form. 



