494 THE TISSUES. 



from the capillaries mainly of the papillae, which subsequently ex- 

 tends to the stratum Malpighii, producing a vesicle; and which 

 finally becomes a pustule, since pus is formed in it. The centre of 

 the pustule is depressed, from the fact that the opening of a seba- 

 ceous gland and a hair-sac penetrates there ; and which does not 

 allow the cuticle there to become detached and elevated, since it is 

 connected with them. 



5. In measles, lichen, and prurigo, papulae alone are produced. 

 There, also, the vascular injection is confined to the most super- 

 ficial layers of the corium. In inveterate cases, however (of pru- 

 rigo), the exudation extends to the deeper layers, and the hairs and 

 sebaceous glands disappear. 



6. In verrucas, or warts, the papilla? become hypertrophied. 



III. The sebaceous glands become, 1, hypertrophied in the akrothy- 

 mion, or moist wart, and in ncevus pilosus. 2. They become atrophied, 

 or entirely disappear, when the hairs fall out, i. e. on bald places. 3. 

 The comedones are mere distensions of the sebaceous glands and the 

 hair-sacs with sebaceous matter, and are most frequent where the 

 glands are largest, as on the nose, lips, chin, ear, areola, and scro- 

 tum. Milium is due to a similar distension of the sebaceous folli- 

 cles alone ; consisting of white spots on the eyelids, the root of the 

 nose, the ear, the scrotum, &c. In both these cases, the apertures 

 are obliterated or entirely closed. 4. Finally, steatoma, especially 

 as it occurs on the scalp, is to be regarded merely as a colossal se- 

 baceous gland distended with its secretion; and atheroma and me- 

 liceris, if occurring in the corium, must be referred to the same 

 category. 



5. The acarus folliculorum residing in healthy and distended 

 hair-sacs and sebaceous glands, has been shown. (Fig. 134.) 



6. New formations of sebaceous glands have been found in an 

 ovarian cyst in connection with hair. Indeed, they may probably 

 occur in any part containing new formations of hair-sacs. A new 

 development of sebaceous glands occurs in cicatrices in the skin, of 

 some years' standing. ( Von Barensprung). 



IV. Of the pathological conditions of the sweat-glands but little 

 is known. In elephantiasis Gra3corum they become hypertrophied ; 

 while they are atrophied in case of corns, and the sweat-duct dis- 

 appears in the outer layer of the cuticle. 



New formations of sweat-ducts occur in connection with those of 

 hair and sebaceous glands, as in ovarian cysts; and in Mohr's case 

 of a large cavity in the lung lined by a membrane in all its ele- 

 ments like the skin (with a subcutaneous areolar tissue under it), 

 and on which hairs, sebaceous follicles, and papillae were deve- 

 loped. 



II. THE Mucous MEMBEANES. 



Mucous membranes line the cavities opening externally, and, like 

 the skin, consist of a corium, a basement-membrane, and an epithe 





