720 DISEASES OF THE SKIN. 



worm crust of the horse producing the favous crust of the dog 

 and cat, and vice versa; but from the foregoing observations, 

 and from the opinion of Bennett, already quoted, that acid 

 secretions favour the development of the favous crust, and from 

 microscopic researches into the identity of the parasites, I am 

 almost inclined to conclude that the ring-worm of the horse may 

 be the favous of the cat and dog, and that the yellow crust of 

 the latter animals, and the more rapid development of the 

 fungus, are due to the natural acid condition of their cutaneous 

 excretions. ^ 



The following woodcut of the microscopic anatomy of the 

 parasite of ring-worm is from original drawings by Professor 

 Vaughan of this College. The scab from which the specimen 

 is prepared was removed by me from a carriage horse, the pro- 

 perty of David Corsar, Esq., of Arbroath. The ring- worm, a soli- 

 tary patch, was situated on the off-side hind quarter, and pre- 

 sented the usual appearance of the affection, namely, a round, 

 baldish patch, covered by a greyish- white crust. 



Treatment. — The treatment of ring-worm, like that of favus, 



^ The opinion I had ventured to express as to the identity of Tinea fav^osa and 

 Tinea circinatus, and that the colour of the crust depended upon the constitution 

 of the animal, was very fortunately confirmed by Mr. M'Gillivray of Banff, in an 

 admirable paper on Porrigo, published in the Veterinarian for March 1872. After 

 reading Mr. M'Gillivray's paper, I took the liberty of asking him a few queries 

 upon the subject ; and I feel I can do no better than publish the answer I received 

 by return of post : — 



" No. 4 Bridge Street, Banff, Qth March 1872. 



' ' My dear Sir — Your letter came to hand this forenoon, and it gives me the 

 most sincere pleasure to answer your queries, as follows : — 



"1. As a rule, yellow crusts are not found in ring- worm in horned cattle. I 

 have, however, seen genuine favous crusts in two such cases. 



" 2. Contagious materiel from the grey crust of cattle or horses undoubtedly (in 

 60 far as my experience goes) produces often, but not invariably, the characteristic 

 yellow crust of favus in the human subject. 



" 3. The crusts or scabs of Porrigo in the dog are generally greyish in colour. 

 In the cat I have invariably found them of a very bright yellow. In the hare I 

 never saw them otherwise than greyish to the naked eye. 



'* So much for your ' queries.' My own candid opinion is that the class of the 

 animal has a good deal to do with the colour of the superincumbent crust or scab 

 of porrigo or tinea. This is the only satisfactory way of accounting for the fact of 

 grey crusts in cattle producing yellow crusts in man. 



" I am, my dear Sir, faithfully yours, 



"Alex. M'Gillivray." 

 "W. Williams, Esq., 



Principal, Veterinary College, Edinburgh.'* 



