788 VEGETABLE PARASITIC SKIN DISEASES. 



tion is afforded for the growth of these by certain conditions 

 extrinsic as well as intrinsic. Youth seems to predispose 

 animals, particularly of certain breeds ; and damp, with dark- 

 ness of location and improper dietary, tend to favour the 

 certainty of the sowing. 



Symptoms. — The early indications of the disease are an open 

 and altered condition of the hair over circumscribed, more or 

 less perfectly circular patches, with a perceptible elevation of 

 the superficial epidermic scales. As the hairs break off and 

 are cast, the skin may show minute vesicles, papules, or pus- 

 tules ; or there may be simply an extra amount of distinct and 

 separable scales, evenly or with slightly elevated edges spread 

 over the parts. 



In some, the entire circular patch or patches — for there are 

 generally several — are denuded of hair, and evidently evenly 

 affected — ' Tonsurant ;' in others, with a greater circumferential 

 margin, there exists a healthy spot in the centre — ' Circinate.' 

 These patches are usually scattered over the upper part of the 

 trunk, and give rise to a trifling amount of itching. Gener- 

 ally disposed to extend, we sometimes meet with cases havmg 

 a natural disposition to cure themselves, which they seem to 

 do through the death of the iricophyton, which evidently 

 perishes from want of sustenance. 



(h) Tinea Favosa — Favus — Yellow or Honeycomb Ringworm. 



Definition. — An epiphytic cidmieous disease characterized 

 hy the appearance of cup-shaped yelloioish-coloured scabs or 

 crusts, sometimes sepo.rate and distinct, at others aggregated 

 and confluent ; these yellow crusts, consisting of a vegetable 

 fungus — Achorion schonleinii — and. capable of transplanta- 

 tion from one animcd to another. 



Pathology, a. Nature. — This, it would appear, is dependent 

 upon or consists in the growth and development in the hair- 

 follicles external to the hair proper, and in the epidermic 

 scales of the particular fungus, the Achorion schonleinii. This 

 parasite, like the iricophyton, is made up of the ordinary fungus 

 elemental structures, chiefly spores or conidia3, with a small 

 amount of amorphous granular matter, and having occasion- 

 ally associated with these another and probably distinct 



