THE ORGANS OP SPECIAL SENSE. 



243 



mercurial ointment, acetic acid (glacial), tincture of can- 

 tharides, Unguentum Argenti Nitratis, sulphurous acid 

 lotions, and many other substances, either of which will 

 prove successful in removal of the parasitic disorder if 

 carefully applied. This disease must not be confounded 

 with herpes circinatus, a non-parasitic disease in which 

 vesicles form over small circular patches, especially in young 

 dogs. As a result of teething or indigestion herpes is rare 

 and soon disappears spontaneously. 



Tinea Favosa v. Favus v. Honeycomb Ringworm differs 

 from the above in the habit of growth of the fungus, 

 Achorion ScKonleinii v. Tricho. favosa, which gives rise to 

 it. This parasite, when it has gained contact with the 

 surface of the body, enters the hair-follicle and developes 

 in and about the hair. At first it causes a slight epithelial 

 proliferation around its base, then the hair (itself diseased) 

 becomes the centre of a cup-shaped crust of a sulphur 

 yellow colour. In advanced cases these crusts become 

 confluent and form an ugly shapeless tumour, sometimes 

 of enormous size, consisting of fungal elements and causing 

 absorption of the tissues against it by pressure. The mass 

 smells like cat's urine, and usually grows on the head of 

 the dog, such being probably the result of the dog catching 

 the disease from affected mice. In treatment all affected 

 hairs and favus crusts should be carefully removed, not 

 with the finger-nail, and destroyed by fire ; the exposed 



Pia. 75. — Achorion Sch5nleinii in early 

 stage of development, mixed with epi- 

 thelial scales (Bennett). 



Fia. 76. — Achorion in more ad- 

 vanced stage from centre of a 

 favus crust ( x 300). (Bennett.) 



