300 THE GROUSE IN HEALTH AND IN DISEASE 



remarkable numbers in the Grouse. The tapeworm Hymenolepis microps 

 alone of these shows any relation in its seasonal prevalence to 



Effect of . ' 



tapeworms " Grouse Disease. This worm, according to our experience, is 



on health. n . . 



undoubtedly very numerous in the spring and autumn, the seasons 

 when " Grouse Disease " is most frequently observed, 1 and practically dis- 

 appears from the bird during the winter months. On the other hand, it has 

 not appeared to be more numerous in diseased than in healthy birds. 



Davainea not infrequently occurs in such enormous masses as to distend 

 the gut. 



Neither of these tapeworms has been found associated with any constant 

 or serious lesions. Davainea appears to us to be the less objectionable. 

 Hymenolepis, whose seasonal prevalence more closely agrees with that of 

 " Grouse Disease," seems to us more likely to be harmful. The large masses 

 in which it often exists in the narrow duodenum appear not unlikely to 

 interfere mechanically with the free passage of food material. Both worms 

 probably make a considerable demand for their own sustenance, even if they 

 do not exert a more serious injurious influence. 



The case against the nematode, Trichostrongylus pergracilis, is much 

 clearer, for though it is seldom entirely absent from healthy birds, neverthe- 

 less, definite lesions in the caecum are often associated with its 

 nematodes presence in large numbers. It probably, however, does little harm 

 if not too numerous. With regard to the presence of this parasite 

 in large numbers in some of the birds caught on the moor, and supposed to 

 be normal birds, it must be remembered that strong wild Grouse are difficult 

 to catch, and that some at least of the methods of capturing Grouse alive 

 seem calculated to catch the weakest birds rather than the stronger ones. 

 On the other hand, we have counted the Strongyli in a number of "normal" 

 and diseased birds, and have found, on the whole, a great difference between 

 the two classes ; very large numbers being always found in the diseased 

 birds, much larger indeed than those found in all but the exceptional members 

 of the healthy class ; and these, for reasons just stated, may perhaps be not 

 normal at all but suffering from the early stages of "Grouse Disease." 



These nematodes, in birds picked up dead or brought to us by the keepers 

 as suffering from " Grouse Disease," are, so far as our experience goes, almost 



1 It is questionable whether there is ever a true outbreak of " Grouse Disease " except in the spring. 

 Sickly birds observed in August and September are now believed to be birds recovering from the spring 

 outbreak, vide chap. iii. p. 49, chap. v. p. 128. 



