"GROUSE DISEASE " STRONGYLOSIS 245 



the end of February and beginning of March, there is com- 

 paratively little mortality among Grouse. 1 As time goes on, 

 however, the infection becomes more and more intensified, 

 for not only do the larval nematodes assume their most active 

 form, but those which have been eaten by the Grouse at the 

 beginning of the period have had time to produce eggs in the 

 intestine of their host, and these eggs are in turn distributed 

 over the moor to add to the infection. The unhealthy conditions 

 do not result in immediate mortality it has been shown by 

 experiment that the birds which have been fatally infected 

 may not die for many weeks. 2 In some cases a severe infest- 

 ment does not result in death. 3 Even in March the mortality 

 has not reached its height, 4 for the majority of birds fatally 

 infected in March will probably not die till April. The infection 

 of the ground goes on with growing intensity, and if the same 

 conditions were prolonged for another month or two it is possible 

 that on the majority of moors hardly a bird would survive. 

 Fortunately the advent of spring brings a blessed relief to the 

 plague-stricken stock, and with the first appearance of new 

 heather growth at the end of April and beginning of May the 

 risk of new infection is past. 



Thus it is that in April the infection reaches its climax, 

 but the birds which die in April are probably the result of 

 infection in March, whereas the birds infected in April die in 

 May, even although the conditions have improved. 



1 Vide Table VI., p. 239. 2 Vide p. 234. 



3 Vide, p. 240. 4 Vide Table VI., p. 239. 



