]SO 



VEGETABLE PARASITES. 



Pustules and favi may be thus distinguished : 



Favi. 



Colour of brimstone,, with a 

 very distinct alveolar depression; 

 rarely discharging a drop of pus 

 when pricked ; easily detached 

 from the skin ; the epidermal 

 layer which covers them is more 

 resistent and has underneath a 

 second thin layer,, thus placing 

 the fungus between two epi- 

 dermal layers ; the development 

 of the favus-contents is very 

 rapid and regular, and may be 

 continued infinitely. 



Pustules. 



Colour whitish or slightly 

 yellowish ; surface even, or 

 slightly convex, with a scarcely 

 perceptible depression at the 

 basis of the hair ; discharging 

 matter on application of a 

 slight pressure or on pricking 

 with a needle, which spreads 

 also into the areoli of the 

 corpus mucosum of the skin ; 

 covered with an extremely thin 

 epidermal layer ; the bottom of 

 the pustules is formed by the 

 papillary bodies of the skin. The 

 change of the pustulous con- 

 tents is less rapid and regular, 

 and, as is the case with all dis- 

 eased products, it becomes hard, 

 forms crusts, and does not grow 

 any more. 



A transition of the favus into pustules, either by continuity or 

 contiguity, has, moreover, never been established. Cases where 

 the centre is formed by a fungus are most liable to be 

 confounded when this centre is surrounded by a purulent ring, 

 without its ever mixing up with the former, a case which may 

 best be studied in Porrigo scutulata. 



It is further of importance in diagnosis, that the three species 

 of glands occurring on these parts of the skin should be con- 

 sidered. 



1. Perspiratory glands, or follicles with a spiral tube, opening 

 on the surface of the skin. 



2. The sebaceous follicles, which do not branch, but end in a 

 sack; simple grape-like glands, which have wrongly been called 

 folliculi sebacei, and which secrete the sebum. They open on 

 the surface of the skin, often in conjunction with the opening of 

 a hair-follicle, which fact was denied by Bazin without giving anv 

 reason. 



