Touching on the very vexed question of the cause of disease, I will say
very little; as to its effects I have said a great deal.
If the poultry fancier keeps a lot of old birds about him, or too thick
upon the ground, disease breaks out amongst them.
I take it that on all moors at the end of six and seven years after
the last attack, there will be a lot of old birds, and, as with the
poultry, disease breaks out and is contagious, and Nature asserts her
rights for the survival of the fittest.
The districts west of Dunkeld are probably the healthiest in all
Scotland, and so there birds resist disease, but disease has even there
made a clearance, and will again.
Yorkshire grouse are now all driven; the old birds come first and
are killed off, and we all know that since driving came into vogue,
Yorkshire birds are far more healthy.
Were it permissible to hunt the ground in the northern Scotch counties
at end of July, and kill off the old birds of the brood, which could be
readily done, it would probably stamp out, or at any rate, postpone,
the attacks of disease.