388 MORBID ANATOMY OF THE SKIN. 



without, is comparatively rare. Any substance which could not 

 be expelled and pushed aside by the vigorous advance of the 

 o-rowinfif hair, Avould have to be endowed with a very extra- 

 ordinary degree both of penetrating power and viscosity. A far 

 more important cause of retention is the over-secretion of epi- 

 dermis and tumefaction of the subepidermic connective tissue 

 about the mouth of the hair-sac, to which allusion has been made 

 above. In one of the disorders which we shall have to consider^ 

 ^ iz. acne, both of these phenomena are simultaneously produced 

 by one and the same cause, sc. a subacute inflammatory state ; 

 and it seems fair to assume a like mode of causation in other 

 eases Avhich are complicated by inflammation. All these causes 

 however, sink into insignificance in the face of a circumstance 

 which throws the very question as to the mechanism and causes 

 of occlusion into the remote background ; I mean the circum- 

 stance that the structure of the hair-sac affords the most favour- 

 able opportunities for an accumulation of secreted matter, without 

 nny previous occlusion of the efferent duct. 



The hair-sac {see fig. 109) is club-shaped in form; the 

 diameter of its fundus exceeds that of its mouth ; its walls face 

 pnrtially downwards ; indeed that portion of the follicular w^all 

 which immediately surrounds the hair-root, may be decidedly 

 said to be turned awa^ from the surface of the skin. Hence 

 the secretions from the wall of the follicle find their escape 

 hindered by that wall itself. It is only the vigorous growth of 

 the hair which prevents the cells shed by the epidermic lining of 

 the follicle, from remaining in its interior. The hair drags- 

 them with it as it grows ; the upward and outward direction 

 of the little scales of its cuticle contributing to this result. The 

 hair may be said to scour out the little recess in which it grows. 

 But it is obvious that this self-cleansing apparatus is only 

 adapted to cope with a very moderate amount of epidermic 

 desquamation on the part of the follicular lining. The least 

 increase of this must necessarily lead to the retention of the 

 secreted matter. Accordingly the question as to what stops up 

 the follicle becomes futile. We ought rather to inquire how it 

 is that the secretions are not usually retained — considering the 

 peculiar structure of the hair-sac. In my opinion, this is the 

 point of view which we ought to take up, with reference to the 

 etiology of retention in the hair-follicles, which is otherwise so 



