570 ON THE ROT IN SHEEP. 



April 7tli^ is the same whichever animal is the one to be blamed, 

 or if both are. And in confirmation of what I there recommend 

 let me say that rot is comparatively rare in the Lake district, 

 while the pasturage of ducks and geese on marshy ground is a 

 branch of agricultural industry greatly developed. It was with 

 much pleasure that I saw two large flocks — one of ducks, the other 

 of geese — echelonned some hundred yards or less apart on such 

 ground there. They will keep down both black and gray slugs as 

 fast as they appear, without, so far as is known^ incurring any 

 danger from this fluke. 



^ [In this letter he recommended the employment of birds, especially ducks, for the 

 destruction of the snails. As sheep lick up snails for the sake of the relish which 

 their salt taste imparts, he recommended that blocks of rock salt should be placed 

 convenient for the sheep to get at. — Editor.] 



[The publication of the above as a letter in the 'Times' of April 14, 1880, induced 

 the Royal Agricultural Society of England to offer a grant to Dr. Rolleston for an 

 investigation into the life-history of the liver-fluke. Dr. Eolleston was unable to 

 undertake the research, but recommended to that Society one of his pupils and 

 demonstrators, Mr. A. P. Thomas of Balliol College, who commenced the investiga- 

 tion on June 7, 1880. The results of his enquiry have been incorporated in pre- 

 liminary reports to the Eoyal Agricultural Society ('Journal,' vol. xvii* 1881, p. i ; vol. 

 xviii. 1882, p. 439), and in 'Nature,' vol. xxvi. p. 606. Mr. Thomas communicated 

 more elaborate memoirs to the Royal Agricultural Society of England, October, 

 1882, printed in their 'Journal,' vol. xix. S. S. part r, under the title 'The 

 Natural History of the Liver-fluke and the prevention of Rot;' and to the 

 •Quarterly Journal of Microscopical Science,' January, 1883, under the title 'The life- 

 history of the Liver-fluke (Fasciola hepatica).^ The conclusion at which he has 

 arrived is that the Lymnaeus truncaiulus is the only English mollusc which can serve 

 as intermediate host to the liver-fluke, though it is possible that in other countries 

 some other mollusc may be the intermediary. It was at one time thought that, 

 although Fasciola hepatica occurred in Australia, the genus Lymnaeus did not exist 

 there. Mr. W. Hatchett Jackson has directed my attention to a paper by Mr. E. A. 

 Smith, 'On the Fresh-water Shells of Australia,' in the 'Proc. Linnaean Society 

 (Zoology),' vol. 16, p. 255, in which he enumerates eleven species of I/ymnaeus, one 

 of which, L. victoriae, is almost identical with L, truncatulus. — Editor.] 



