328 THE GROUSE IN HEALTH AND IN DISEASE 



that the stock has been congested on any portion of the 

 ground. 



It must be clearly understood that " Grouse Disease " is 

 not dependent on any fixed number of Strongyles in the caecal 

 intestines, or that any fixed standard of power of resistance 

 guarantees immunity from the disease, but rather that the 

 epidemic depends on the relation between the amount of 

 infection and the power of combating the same. That is to 

 say, that the nematode infection which would be fatal to the 

 weak bird might conceivably be the normal burden of the 

 strong Grouse ; and that the same bird might carry with ease 

 in autumn -when well nourished and fully feathered the 

 number of Strongyle worms to which he would succumb in 

 spring when light in weight and short of food. If we realise 

 this theory in its entirety we shall find ourselves on vantage 

 ground from which the many and apparently contending aspects 

 of " Grouse Disease," and the numerous hypotheses based 

 thereon, can be readily explained. 



CERTAIN THEORIES OF DISEASE HELD BY SPORTSMEN AND 

 FIELD OBSERVERS. 



First Theory. A very common theory, especially on the 

 west coast of England and Scotland, is that frost is the cause of 

 " Grouse Disease." This theory is usually stated in the form 

 that " the frost of early spring browns the heather, birds 

 eat the heather and die of indigestion." This is a very good 

 example of an incorrect deduction drawn from properly observed 

 natural phenomena, and of the ease with which secondary 

 causes are confused with primary ones. It is quite incorrect to 

 say that frost in spring is the immediate cause of " Grouse 

 Disease," for the very excellent reason that of nearly two 

 thousand crops examined by the Committee not one single 

 crop has been found to contain a shoot of brown or frost-dried 

 heather. It is, however, correct to say that when frost comes 

 in late spring, or when the cold east winds scorch the young 



