306 MORBID ANATOMY OF THE SKIN. 



plastic infiltration assumes such proportions, the accumulation of 

 pus-cells is so dense, that the blood-vessels undergo compression. 

 In one variety of the furunculus, the Anthrax, this goes so far 

 as actually to cause the death of the infiltrated part, which grows 

 as black and dry as boot-leather ; in ordinary furunculi the 

 process does not go beyond simple necrobiosis ; many of the cells 

 show signs of fatty degeneration. In either case, however, the 

 mfiltrated part is gradually cut off from the surrounding con- 

 nective tissue by a process of suppurative demarcation, and 

 expelled from the skin — a termination usually hastened by opera- 

 tive interference. It constitutes the familiar "core" which, 

 when teazed out under the microscope, exhibits nothing beyond 

 disintegrating cells and a few fibres of connective tissue amid a 

 mass of debris. After the expulsion of the core the sinuous 

 ulcer which remains, heals by the second intention, leaving a 

 stellate scar. 



y. Hypertrophy. 



§ 338. Active enlargements of the hair-follicles, due to morbid 

 growth, must be distinguished fi'om their passive enlargement, 

 due to retained secretions. Next, they must themselves be 

 divided into true and ftilse hypertrophies ; the former retaining 

 the original anatomical and physiological character of the parts ; 

 while in the latter, the increase in size is associated with some 

 specific modification of structure which arrests their normal 

 functional activity. The hair-sacs and their appended glands 

 thus become foreign to the organism ; they pass into the category 

 of heteroplastic tumours. The consideration of these "false" 

 hypertrophies will therefore be deferred for the present. 



§ 339. A true " overgrowth of hair" can only be said to 

 exist in hairy moles, the so-called "mice" (iicevus spilus). 

 These brown, hemispherical or flattened elevations of the skin, 

 sometimes of considerable size, would seem to offer peculiar 

 facilities for the most luxuriant growth of hair. Not only are 

 the individual hairs very stout, but, if we happen to possess a 

 mole of om' own, we notice that its hairs are shed and renewed 

 much oftener than those of the head and beard. If we make a 

 vertical section through one of these nsevi, we find at least one- 

 fom'th of the hair-follicles, which are very thickly set, furnished 



