226 SPECIAL HISTOLOGY. 



niculus adiposus. If these innermost cells, which rarely 

 exhibit any nucleus, are traced onwards towards the excretory 

 duct, nothing is more easy to observe, than that similar 

 cells, applied uninterruptedly one to the other, are continued 

 into this also, i. e., into the canal lined by its epithelium ; 

 then, entering the hair-sac, they occupy the space between 

 the hair and the epidermis of the hair-sac, and are finally 

 extruded. These cells are the sole sources of the cutaneous 

 sebaceous matter, a substance which, when fresh and at 

 the common temperature, is semifluid, but in the dead sub- 

 ject more consistent, like butter or soft cheese, whitish or 

 whitish-yellow in colour, sometimes viscid, at others friable. 

 Its cells, in the fresh secretion, adhere together more or less 

 closely, and are thence generally flattened and irregular in 

 form ; their membrane is not recognisable, and their con- 

 tents are quite homogeneous, and transparent, with a yellowish 

 hue. If dilute alkalies, however, be added, they swell up 

 after a short time into beautiful round or elongated vesicles, 

 in which, in consequence of the penetration of the reagent, 

 the fat divides into separate drops of various sizes, and into 

 irregular masses ; at the same time the sebaceous matter 

 becomes white, owing to the numerous minute fatty particles 

 which are produced, and larger fat drops are formed, probably 

 in consequence of the solution of many cells. Besides that 

 in the cells, the sebaceous matter also contains free fat, in 

 larger or smaller quantity, and in some cases, perhaps, an 

 excessively minute amount of a clear fluid. 



It appears, then, that the cutaneous sebaceous matter is a 

 secretion, consisting, so to speak, only of formed elements, 

 either cells containing fat alone, or cells together with drops 

 of fat. These constituents are formed in the vesicular ends of 

 the glands, in consequence of a production of cells, which, as in 

 the epidermic tissues in general, proceeds entirely from the 

 pre-existing cells, unaided by free cell-development, of which 

 there is in this case no indication. By endogenous develop- 

 ment round portions of contents, or by division, cells are con- 

 tinually produced at the bottom of the glandular vesicles. 

 These are at first pale, and contain but few granules, like the 

 epithelial cells from which they arise; but as they are forced 

 towards the interior by cells developed after them, they are very 



