Etiology. 919 



portance. First of all the favus fungus, contrary to Tricophyton ton- 

 surans, needs a large amount of protein for its nourishment while on 

 nutritive media containing only carbohydrates its growth is very 

 scanty. It thrives best at 25° C, although some of its varieties develop 

 at lower temperatures; below 10° C. its growth ceases. The fungus 

 forms, on all culture media, moss-like shoots which start from the 

 periphery of the growth and it inclines almost exclusively to deep 

 growth. On gelatine it forms a deposit which somewhat resembles 

 that of tricophyton, but the medium is liquefied only in the course of 

 the second month. On potatoes and beets the growth is perpendicularly 

 raised from the culture. It appears bunched, grayish white and finally 

 grayish yellow. The cultures grown on most solid culture media yield, 

 after short drying (3 or 4 days in the exsiccator), a mortar-like, brittle, 

 yellowish mass. The fungus develops best in 2% meat peptone agar at 

 body temperature (Krai). According to their age and origin as well 

 as also according to the nature of the culture medium, the cultures of 

 the favus fungus exhibit a similar pleomorphism and the same vari- 

 ability as was discussed in connection with Tricophyton tonsurans 

 (Krai, Plant, Walsch, Tischutkin). Consequently it is possible for the 

 favus fungus under the influence of different conditions of life, to form 

 varieties which have certain characteristic peculiarities and which 

 are transmitted by cultivation, but which may be changed to their orig- 

 inal form by passage through other kinds of skin. 



On the ground of cultured peculiarities several kinds of fungus have been 

 distinguished which are said to share in the production of favus. Thus Quincke 

 found three different fungi, described by him as a, j8 and y. The first and third 

 were transmissible to man and animals (the second was renounced later on by 

 Quincke himself). Also Frank as well as Unna have demonstrated three different 

 kinds of fungi and later on nine kinds were described by the latter author. 

 Sabrazes further maintained that the favus disease of man is caused by the 

 Achorion Schonleinii and that of dogs by a different fungus, the Oospora canina. 

 E. Blanchard also considers man, dog and mouse favus as three different diseases. 



As the investigations of Krai, Plant, Mibelli, Pick, Wiilsch, Tischutkin and 

 others have proved, the alleged multiplicity of the favus fungus can readily be 

 explained by its pleomorphism. Favus disease consequently must be considered as 

 a uniform disease, which conclusion is supported by the possibility of a mutual 

 infection. 



Plaut distinguishes two principal types of the pure culture: 



1, The wax type, characterized by yellowish growths of wax-like nature, with 

 radiating folds and central elevations. To this type belong the ^ and y fungus 

 of Quincke, Achorion dikroon of Unna, Krai's fungus, the fungus of human favus 

 Sabrazes, etc. . , , . , ^ .^, 



2. The downy type, characterized by white discs covered with high down, with 

 central irregular elevations; the color is variously snow white, yellow or red. This 

 forms a connecting link between the favus and tricophyton fungi. To this type 

 belong the a fungus of Quincke, the Achorion eutythrix of Unna and the organism 

 of mouse favus. 



Pathogenicity. After artificial transmission, the favus 

 fungus localizes much more readily in young animals than in 

 older ones. Dog favus was transmitted by Sabrazes to man, 

 mice and rabbits ; cat favus by Saint-Cyr to cats, mouse favus 

 by Schindelka to dogs, cats and chickens, favus of man by the 

 same author to dogs, cats, cattle, horses and asses. 



While the transmission of mouse favus led to disease which was almost like 

 the natural affection in the dog the inoculation of the human favus led m only 

 one case to onychomycosis (the surface of the skin remained healthy) while m cats 

 characteristic scutula developed and on the comb of fowls roundish scaling discs 



