ACHORION SCHOENLEINII. 165 



has been wrongly stated that these formations have their seat in 

 the principal part of the follicle of the hair, or of the glandulse 

 sebacea3. At the spot which has been freed from the favus there 

 remains a smooth impression red from irritation, which, how- 

 ever, soon disappears, often in the course of an hour, in con- 

 sequence of the elasticity of the skin when freed from pressure. 



Structure of the favi. In order to study carefully the structure 

 and construction of the fungus, it is well to examine, first, the 

 normal structure of the shaft of the hair, which is thus described 

 by Gudden. The shaft of the hair and the inner sheath of the root 

 consist of a modified epidermis composed of bright transparent cells, 

 which are round below, becoming flat towards the upper part, and 

 stretching out to a considerable length, parallel to the shaft, 

 perhaps even losing their nucleus, whilst the layer of epidermis 

 of the skin consists of smaller round or elongated cells. This 

 may be seen best by drawing out the shaft of the hair, together 

 with its inner sheath, and separating it from the epidermal layer 

 of the skin. Since this does not always succeed, the layer of 

 epidermis of the skin may be torn off by means of a curved 

 and not too sharp couching-needle, and split longitudinally, 

 when the single cells are usually brought out very distinctly at 

 the edge. 



The favus is hard, dry, brittle ; its fracture is shining ; its in- 

 terior whitish-yellow, and paler than the outer surface. When 

 examined with a lens, it is seen to be spongy, or even a little 

 hollow in the centre (Lebert) ; when seen under stronger powers, 

 its contents appear to be the tougher the nearer they approach 

 the surface, forming a thin, dense layer, which acts as a kind of 

 cover. 



The exterior layer = " stroma" = " gangue amorphe," is one 

 sixth of a millimetre in thickness, forming a finely granulated 

 amorphous mass, representing a membrane which cannot be 

 isolated, belonging, nevertheless, to the favus, and is not the 

 result of the drying up of the amorphous, albuminous, exuded 

 mass, nor of an accelerated formation of the epidermis, nor of the 

 drying up of the pus or the mixing of anyone of these substances 

 with the other. It forms the amorphous, homogeneous, very finely 

 granulated stroma, consisting of organic substances or the gangue 

 amorphe common to all fungi. 



The inner surface of this outer layer passes gradually into the 

 central part ; it is spongy, easily rubbed to a yellowish-white dust, 



