COMEDO. 389 



-enigmatical. The starting-point of the disorder consists in 

 over-secretion from the follicular lining ; and this serves also 

 to explain the occurrence of retention. In the majority of 

 instances the over-secretion in the hair-sacs is merely a part 

 of a general disorder of the whole cutaneous surface, in which 

 its recesses take part in their due measure. Persons whose 

 skins are naturally greasy, whose hair and nails grow fast, whose 

 heads are always full of scurf — young men at the time of puberty 

 — are therefore specially predisposed to diseases caused by 

 retention of secretions in the hair-sacs. Moreover we often 

 find them in the neighbourhood of epitheliomata and warts — 

 wherever indeed a proliferation of cuticular elements is an 

 essential feature of the anatomical alterations. 



§ 329. Granting therefore that we have to do with over- 

 secretion in the interior of a hair-follicle, we next proceed to 

 inquire whether this affects the follicle in its entirety or only a 

 portion of it. The former is the case in comedo. This term is 

 applied to a condition in which the entire length of the hair-sac 

 is uniformly distended by an accumulation of epidermic pro- 

 ducts. The skin may easily be raised from its bed at this point. 

 If we squeeze it firmly on each side of the comedo, a small 

 whitish plug is driven out of the sac, which exhibits a black 

 spot on its free end, and has accordingly been compared to a 

 living organism — a maggot — (comedo). Of course, the appear- 

 ance in question is due to the impregnation of the free end 

 with dirt from without. If we put the plug in a drop of 

 water and examine it microscopically, we find nothing beyond 

 epidermic scales, which here and there exhibit an opaquely- 

 dotted appearance due to the presence of oil-globules. Besides 

 this we find free oil-globules, furnished by the sebaceous glands. 

 According to Gustav Simon a very small six-legged parasite 

 with a long abdomen, the acarus foUiculorum^ is more common in 

 these than in normal hair-sacs. I have never seen it. Come- 

 dones are usually found on the alge and bridge of the nose, 

 and on the shoulders — wherever the skin is coated with down 

 only. They do not affect the hair-follicles of the scalp and 

 chin. 



§ 330. If the over-secretion is restricted to the fundus of the 

 sac, the resulting appearances are somewhat different. The 

 epidermic masses form concentric laminse round a central nucleus, 



