I16 BACTERIOLOGICAL DIAGNOSIS. 
and by the fact that they lie within the hair, the cuticle 
of which usually remains intact (fig. 21). 
This fungus is a rare cause (in this country) of ring- 
worm 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. 
Fig, 22.—Trichophyton ectothrix from a case of kerion. 
The tvichophyton 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. 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 (fig. 22), 
In some cases this organism does tend to invade the 
hair, and in this case the name “endo-ectothrix”’ is 
applied to it. 
