12 THE GROUSE DISEASE chap, i 



specific and readily understood manner ; but this fact 

 will not explain the nature of the cause or disease 

 which operates so fatally, without any exceptional 

 development of parasites, and certainly without the 

 slightest appearance of inanition or other concomitant 

 symptoms of helminthiasis. Outside the parasitic 

 hypothesis, applicable as that theory is to a certain 

 class of cases, there lies, I am convinced, the great 

 bulk of fatal instances, the exact cause of which fatal- 

 ity must be sought for in some lesion analogous to that 

 involved in the idea of the epidemic theory. We 

 must thus account for the death in numbers of grouse 

 which, with what one may consider a normal and 

 actual degree of parasitism, yet die and succumb to 

 disease, and which on examination present well- 

 nourished bodies, firm, healthy, muscular tissue, and 

 other signs of presumed health " (Macdonald, pp. 

 147 and 148). 



