DISEASES OF THE SKIN. 735 



•worm crust of the hoi-se pixDJucing the favous crust of the dof 

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

 and from the opinion of Bennett, ali'eady quoted, that acid 

 BBcretions favour the development of the favaus 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 follo%ving 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 Coraar, Esq., of Arbroath, The ring-worm, a soli- 

 tary patch, u^s situated on the off-side hind quarter, and pre- 

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

 baldish patch, covered by a gre}-ish-white crust. 



Tvtatmeni. — The treatment of ring-worm, like that of favusj 



* The opinion I had ventured to exi^reM as to the identity of Tinea favosa ancf 

 'iXnea circinatua, and that the colour of the crust depended upon the oonstitutictfi 

 c: the animal, waa very fortunately confirmed by llr. M'Gillivray of Banff, in an 

 admirable paper on Porrifro, published in the ] eterinarutn for llaich 1872. After 

 reading llr. M "GiUivray'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 pc«t : — 



" No. 4 Beidob Stujbt, BiNrr, 6(A J/arcA 1872. 



" IIt deab Sib — Your letter came to hand this forenoon, and it g^ves me til* 

 moat sincere pleasure to answer jour queries, aa foUoTVs : — 



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

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



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

 BO far as my experience goes) produces often, but not invariably, the characterlsac 

 yellow cruflt of favus in tht human ivbject. 



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

 In the cat I have in^a^iably found them of a very bright yellow. In the kare I 

 never saw them otherwise than greyiah 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'Gilutrat.* 



" W. Williams, Eeq,, 

 Principal, Veterinary College, Edinburgh.'* 



