326 THE GROUSE IN HEALTH AND IN DISEASE 



together by stress of weather or shortage of food, that the number 

 of Strongyles will increase by geometrical progression as the 

 birds get more heavily infected and therefore increasingly able 

 to foul the moor, it is not difficult to realise, despite the countless 

 thousands of larvae destroyed by drought, mishap, heather- 

 burning, etc., how the moor may become more and more tainted, 

 until at last every shoot of heather bears the seeds of " Grouse 

 Disease." 



Equal in importance to the presence or absence of the 

 Strongyle is the second factor, the power of resistance of the 

 individual Grouse. The fact that the normal Grouse, in the 

 proportion of ninety-five to five, has its caeca charged with 

 Strongyle worms shows that, under a certain set of natural 

 conditions, the worms are not necessarily hurtful to their host. 

 Upset the natural balance, and this at once ceases to be the case. 



This varying power of resistance of the host to parasitic 

 or bacterial infection has long been a recognised commonplace 

 of science. 



Recent scientific investigation seems to indicate that the 

 power of resistance varies directly with the health of the subject, 

 and as far as the Committee's investigation goes, the Grouse 

 appears to be no exception to the rule. A bird in full health, 

 weight, and plumage can carry his quota of Strongyles like an 

 alderman his wine ; but once allow the vitality or weight to 

 go below a certain recognised figure, then immediately the 

 Strongyle worm appears to operate harmfully on the vitality 

 of the bird. The caeca become inflamed, the digestive process 

 is no longer effective, the moult is delayed so that the bird loses 

 the fresh colour of its plumage, it declines in weight, and, after 

 a more or less protracted resistance, eventually succumbs. 



Without going into the whole argument in support of these 

 statements it is only necessary to say that the weight of the 

 bird is the most easily recognised indication of its power of 

 resistance to disease. That nine-tenths, if not all, of the out- 

 breaks of " Grouse Disease " have their origin in the spring, 

 when the food-supply is at its shortest, and when the bird is 



