RINGWORM 99 



they lie within the hair, the cuticle of which usually remains 

 intact (Plate VI., Fig. 2). 



This fungus is a rare cause (in this country) of ringworm of the 

 scalp, and the disease caused by it appears to be somewhat easier 

 to cure than that due to the microsporon, though opinions on this 

 point are divided. It also attacks other regions of the body, 

 causing tinea circinata, or eczema marginatum. 



It always appears to be derived from a human case, and never 

 by infection from animals. 



The T. ectothrix (like the microsporon) forms a sheath round 

 the outside of the hair, to which it is closely applied, like the bark 

 to a tree, but, unlike the small-spored variety, does not destroy 

 the cuticle. The spores are about as large as in the preceding 

 species, and are arranged in chains ; this fact, together with the 

 position of the fungus with regard to the hair, will enable a 

 diagnosis to be made (Plate VI., Fig. i). 



This fungus is a rare cause of ringworm of the scalp, and the 

 disease it causes is readily cured. It also causes ringworm of 

 the body and of the beard region, which the endothrix does not 

 attack. According to Sabouraud (to whose work on these 

 organisms we owe most of our knowledge on the subject), kerion 

 is always caused by this organism, but this is not generally 

 accepted. It appears, however, to be a fact that suppurative 

 lesions (folliculitis, kerion, etc.) are usually caused by this fungus. 



This species is often derived from one of the lower animals, 

 especially from the horse, cat, and dog. 



Favus is caused by a closely allied organism, the Achonon 

 Schonleinii. This may be demonstrated by either of the processes 

 already described. It affects the skin in two ways : by the forma- 

 tion of the characteristic scutula and by the ringworm-like invasion 

 of the hair. The scutulum is composed of vertical mycelial fila- 

 ments, which branch, and which appear to be composed of short 

 rods. There are often oval spores at the free ends of these 

 branches, and, according to Sabouraud, branching into three occurs 

 (trichotomous branching), and is very characteristic, though diffi- 

 cult to see. The radiation of several filaments from one point, 

 and the fact that these appear to be made up of short lengths, 

 gives rise to an appearance which has been compared to that of 

 the metatarsal bones, and the term " favic tarsus" has been 

 applied. 



When favus affects the hair (Plate VI., Fig, 5), the cuticle 



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