DIAGNOSIS OF FAVUS. 179 



not dissolve the pure mass of favi ; they are left unaltered, whilst 

 fatty matters are easily dissolved. The epithelial masses become 

 thin by this treatment. Ammonia renders the favus-mass a 

 little paler, but does not dissolve it, whilst it dissolves pus 

 and impetiginous crusts, forming a milky gelatinous mass. An 

 alcoholic solution of potassa, especially on being heated, dis- 

 solves impetigo-crusts, pus, skin, hair, fatty matter, and sebum, 

 but not the favi. Nitric acid is coloured yellowish-brown by 

 crusts of the impetigo, which, after a few hours, become of 

 a turmeric yellow; masses of favi impart to it a golden-yellow 

 colour, turning to straw-yellow, especially after the lapse of 

 a day. Sulphuric acid attacks favous and impetiginous masses, 

 and is turned reddish ; the crusts of favi, however, become 

 porous, pumice-stone-like; the impetiginous crusts gelatinous. 

 Chlorine gas discolours favous and impetiginous masses, hair, &c. 

 Mouldy formations show the same reactions as the masses of favi. 

 Hebra is of opinion, as already remarked, that favus and Herpes 

 tonsurans are identical ; to which he seems to have been chiefly led 

 by the circumstance that the spores of the favus and of Herpes 

 tonsurans penetrate into the interior of the hair itself; that the 

 favus-fungus, occurring on the body and back and forming scabs, 

 cures itself, like Herpes tonsurans. His opinion that the favus is 

 merely a further stage of development of Herpes tonsurans seems 

 to be principally based upon two cases described in his periodical, 

 one of which having quite the appearance of Herpes tonsurans, 

 exhibiting the favus-fungi, when it was examined under the micro- 

 scope ; the other, however, showing the favus-fungus exactly as it 

 was observed on the head, and in scabs on the top of the nose. On 

 looking closer to the latter case, I am uncertain whether Hebra 

 really understood, by Herpes tonsuram, what we have understood 

 by it; for he does not speak of fungi in the hair, but only of epi- 

 dermal accumulation of scales, the latter being but accidental to 

 Herpes tonsurans. 



The fatty substances of sebum and cerumen exhibit vesicular 

 granules, rhombic crystals, and epithelial cells; the sero-purulent 

 and purulent masses show granulated globules and globules of pus, 

 but are not, however, to be confounded with favi. 



The favus-fungus may be distinguished by the above-described 

 thallus from the ferment-alga, which resembles only the sporidia 

 of the former. 



