NATURE OF THE DISEASE 



whether birds affected with the disease carry it from 

 one locality, not to the one lying next, but to a moor 

 some distance off; whether in one moor there are 

 present conditions as to situation, heather, water, etc., 

 which are favourable or unfavourable to the develop- 

 ment and spread of the disease, — all these are points 

 which may, and probably (see below) do, play a part 

 in the dissemination of the plague. 



A disease which year after year assumes the char- 

 acter of an epidemic at particular seasons, which com- 

 mences as isolated cases, and gradually works itself 

 up into a serious epidemic, i.e. spreads from a few to 

 many individuals, and again in the same way gradually 

 declines ; further, a disease which has such uniform 

 and typical characters, both as to symptoms and 

 pathology ; bears on the face of it the character of an 

 acute infectious disease. 



The late Dr. Cobbold, in his well-known brochure 

 on the grouse disease, enunciated that the cause of 

 the grouse disease is a parasite, in fact a nematoid 

 worm belonging to the group of strongyles i^Stron- 

 gyhis pergracilis), for in the intestines of grouse 

 dead of the disease this parasite was constantly / 

 present. Numerous grouse which he examined, and 

 which succumbed either in the epidemic of 1872 or 

 1873, and others examined in later years, contained 

 these parasites in abundance, though " without doubt " 



