258 



of the cercarian stage of Fasciola hepatica or the common fluke. A 

 change of hosts is essential. 



Scientific Club, April 5, 1880, 



4. On the Rot in Sheep K 



By Prof. G. Rolleston in Oxford. 



The English Lake District presents us with as simple a case for 

 the investigation of the cause of rot in sheep as any other portion of 

 the wide area over which that disease has spread, with, perhaps, the 

 exception of such isolated localities as the Faroe Islands. 



Having occasion to visit the district in question last week, I used 

 the opportunity for making a few inquiries of the farmers and shepherds 

 there as to the natural history of this plague. These inquiries were of the 

 simplest kind, anybody can repeat them, and I cannot but think that 

 the answers he will receive will incline such an inquirer to think that 

 a strong a priori case is made out in favour of the view put forward in 

 »The Times« of April 7, to the effect of identifying the black slug [Arion 

 ater) or the gray slug [Limax agresfAs) as one necessary link in the chain 

 of causes concerned. I found the natives as intelligent and observant as 

 I have found them to be any time during the last 34 years upon natural 

 history questions; and I very rapidly got the following facts deposed 

 to by them without any prompting on my part : — 



1) The fluke disease is a disease of low grounds, and notably of 

 pastures liable to be flooded. 



2) But not exclusively of pastures liable to be flooded ; for, what 

 is of special consequence as going some way towards eliminating the 

 pond snails [Limnaeus pereger) and others from the charge of sharing 

 in the causation of fluke disease, the pasturing of sheep in a stubble 

 rich in the »melancholic poisonous green,« which a wet autumn often 

 produces, is a very sure way for producing the disease. 



3) The words just given in inverted commas are not the exact 

 words employed by my informants; those which follow are, or pretty 

 nearly so — »a single bellyful will give the disease.« 



4) »A pasture will give the disease at the back-end of the year 

 which won't give it after Candlemas.« This means that the winter cold 

 and rains destroy or wash away the larval or other forms of flukes 

 which the slugs brought with them in the autumn. 



The first of these observations is confirmatory, as are all accurate 

 observations on the subject, of the view which asserts that the presence 



»The Times«, of Wednesday, April 14, 1880. 



