398 DISEASES OF THE FEET. 



" Incubation. — The incubation stage is from three to six days. 



" Extension. — The disease is chiefly extended through traffic 

 in sheep at the fairs and markets; by allowing diseased animals 

 to travel in railway waggons and ships, and introducing healthy 

 stock into these without a thorough cleansing having been 

 carried out. Pastures on which affected sheep have grazed a 

 short time previously have also been known to cause the disease 

 in flocks succeeding them. Indeed, we can scarcely realise any 

 more certain mode of extension than that of depasturing healthy 

 sheep with diseased, or where the latter have been a short time 

 before. The grass imbibes the discharge from the suppurating 

 claws, and especially from between them, where it is most 

 abundant and virulent ; and the healthy sheep, walking through 

 the grass, must receive continuous applications of the virus from 

 every blade, and on the very part where experiments have 

 proved the skin to be most prompt and certain in absorbing it 

 — between the toes. 



" Contact between, or mixing of, the sick and healthy, even for 

 a brief period, on roads, at fairs, or on pastures, is also a prolific 

 cause of extension. Litter, fodder, sheds, and stables must also 

 be included among the media which harbour and convey the 

 contagion. As has been remarked, the extension is facilitated 

 by certain external influences." 



I have inserted these quotations in order that the reader may 

 have both sides of the question. 



I think, however, that the direct inoculation, by means 

 of shreds of loose horn or matter from diseased feet applied 

 between the claws of feet that were healthy, proves nothing 

 further than that discharge, in virtue of its imtating properties, 

 induced inflammation of the inter-digital tissues in a manner 

 similar to that which would result from the application of any 

 common irritant, or even a foreign body, applied to and retained 

 in the same place, and that the other facts are incomplete, as it 

 is not stated whether the season was damp or dry. Professor 

 Brown's opinion upon this question is well worth quoting. 

 He says: — " The third position which we have undertaken to 

 discuss will require but little consideration. It refers to the 

 * virus ' of ' foot-rot,' — the animal poison supposed to be capable 

 of inducing the disease by contact. 



" The question of the existence of such poison among the pro- 



