THE GROUSE DISEASE 



October, and later, but their numbers are, for obvious 

 reasons, smaller during this time. That a moor, or 

 even a whole district, is and remains free from the 

 epidemic during one or more years may be, and as 

 a rule is, due to a variety of conditions which also as 

 regards epidemics of other infectious diseases are 

 known to occur; some of these we do know and 

 call secondary or accessory conditions. Assuming 

 the disease to be an infectious disease, there is 

 nothing extraordinary in the fact, occasionally ob- 

 served, and used by some as an argument against 

 the infectious nature of the malady, to wit, that in 

 a given country a series of moors are seriously im- 

 plicated, while here and there one or another moor 

 is only slightly affected, or apparently remains free 

 from the disease. I say there is nothing extraordinary 

 in this because there may be, for all we know, a 

 variety of circumstances at work which favour, or 

 disfavour, the spread of infection from one moor to 

 the neighbouring moor. In human epidemics this 

 fact is observed repeatedly. One locality becomes a 

 hot-bed for the disease ; the neighbouring locality 

 remains fairly free from disease, or has only few cases. 

 In a third locality at a greater distance the disease 

 is again rife, and so on. Whether, in the case of the 

 grouse disease, birds are in better condition to resist the 

 disease in one locality than in the neighbouring one ; 



