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 

 tn 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 {Stron- 

 gylus 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" 



