FAVUS SQUARROSUS. 175 



is spared by the favus, as well as the sebaceous follicles, which 

 are very strongly developed during a powerful reaction of the 

 skin. The renewed growth of the hair of persons who suffer 

 much from favi and the falling off of the hair at the period of 

 puberty, shows that it is seated in the epidermis. The above- 

 mentioned little capsule gradually increases and moves downwards 

 until it reaches the lowest layer of the cutis, where it spreads 

 more luxuriantly in all directions. Its higher edge encounters 

 a still more resistent epidermal layer, projects against it, and 

 forms a yellowish, pretty-looking little nest, harbouring in its 

 cavity, cells and air-bubbles. The capsule is formed when the 

 edges are gradually bent inwards, often leaving only a small 

 opening in the centre. When the scab has once settled in the 

 lower layers of the epidermis, new layers of favi are continually 

 seen to make their way to the light; whilst the lower layers 

 remain unchanged. Their development ceases on drying the 

 filaments, but recommences when they are put into water and 

 soaked. The concentric rings, described by Simon, in scabs, 

 are merely caused by the turning up of the layers of the scab. 

 Sometimes a small opening is seen, in the middle of the disc 

 (Gruby), from which the favus grows, and which was forming simul- 

 taneously with the latter, and is only covered by epidermal cells. 

 The scabs also run together (Porrigo favosa, Favus conspersus}. 

 When the formation proceeds rapidly, and when a crust is 

 formed about every hair, the crusts press on each other, the 

 scabs increase and rise on account of their humidity, between 

 the hairs. Most instructive microscopic preparations may be 

 obtained by detaching the freshly formed scabs, after cleansing 

 the scalp according to Gudden's method (see below). Sections 

 of the older scabs exhibit two layers, separated mostly by a line 

 of demarcation, The thinner, whitish, and crumbling inner layer 

 contains the thallus-threads ; the free and thicker yellowish layer 

 the sporidia and spores. (Remak.) 



Diseased phenomena produced by the favus. Remak experienced 

 no change of general health during the time the artificially created 

 favus was active ; nor is there any change perceptible in strong 

 children, should the disease even last for years. It is, however, 

 very doubtful whether an extensive suppurating favus acts in the 

 same way as other diseases of the head, like the impetigines, 

 which act vicariously, by replacing chronic inflammations and 

 mucous discharges of the conjunctiva, the cornea, and the auditory 



