690 THE PARASITES OF FAVUS 



poplar seeds : then from the centre of the colony a tuft of downy aerial hyphse 

 emerges, forming around the growth a number of glabrous concentric circles 

 which ultimately become slightly downy. The growth is white. 



In these cultures the mycelial filaments are at first short, but later elongate, 

 producing a tangled mass and becoming swollen into club-shaped swellings. After 

 a few days the ends of the mycelial filaments throw out long filaments twisted like 

 the lash of a whip, on which lateral thickenings appear carrying a series of teeth 

 like the teeth of a comb. These are abortive forms of branches. When the parasite 

 is grown on unsuitable media certain of the filaments with club-shaped swellings 

 become isolated by a transverse constriction ; their contents become granular and 

 their walls thicken thus forming organs of resistance or chlamydospores. In cultures 

 on suitable media fructification by fusiform or cylindrical conidia occurs at about 

 the end of a week. 



3. Experimental inoculation. Microsporum audouini appears to be a 

 strictly human parasite. Experimental infection of children, whose scalp is 

 the most favourable situation for the growth of the parasite, is not feasible 

 on account of the contagiousness and chronic nature of the disease. 

 Generally speaking, the lower animals are immune to infection (Bodin), but 

 in a few cases the disease has been reproduced in rabbits, guinea-pigs and 

 horses (Courmont). 



The varieties found in the spontaneous ringworms of the dog and young 

 horse are infective for the lower animals. 



SECTION IV. THE GENUS ACHORION. 

 A. The parasite of favus in man. 



Aehorion schoenleini. 



Schoenlein showed that favus 1 is caused by a fungus 2 belonging to the 

 genus Aehorion. 



Aehorion schoenleini may infect any of the epithelial tissues the hair of the 

 scalp, the skin, the nails ; in one case seen by Kaposi and Kundrat the parasite 

 had infected the mucous membrane of the oesophagus, stomach, and intestine. As 

 a rule the infected hair projects from a small cup-like depression in the centre of 

 the characteristic sulphur-yellow disc or scutulum. The hair is discoloured almost 

 up to its point of emergence, and does not break in the forceps but comes out entire. 



According to Bodin, Neebe and Unna several species of Aehorion are found in 

 human favus all very closely related to one another. Many observers on the other 

 hand hold that there is but one species. 



Attempts to infect the lower animals have given inconstant results. Sabrazes 

 says that he has produced a pseudo-tuberculous condition by inoculating a spore- 

 bearing culture of Aehorion into the peritoneal cavity of a guinea-pig. 



Morphology and methods of detection. 



1. Microscopical appearance. Immerse the hair in a drop of 40 per cent, 

 potash on a slide and cover with a cover-glass. Heat carefully over the 

 pilot flame of a Bunsen until the potash solution just begins to boil, then 

 lay the slide on a cold surface to stop the process of dissociation and 

 examine at once with a low eyepiece and dry lens ; the potash clears the 

 hair and the parasite can be readily seen. 



To make permanent preparations treat with potash as above and then run a little 

 drop of eosin-glycerin under the cover-glass. Hairs which have been boiled in 



[ x The disease is so called from its resemblance to an honeycomb (L. favus). 

 _ [ 2 This perhaps is not strictly true. Schoenlein undoubtedly found a fungus in associa- 

 tion with favus but it seems that Griiby, who independently discovered the fungus, was 

 the first to actually show the relation of cause and effect.] 



