232 THE GROUSE IN HEALTH AND IN DISEASE 



chemical substances would appear at first sight to be a hopeful line of action, 

 but the occurrence of the csecal droppings more or less all over the moor, and the 

 enormous area requiring treatment, render any such methods futile. Moreover, 

 as we have shown, the larvae after a brief period of development ascend the 

 heather and can remain hidden in the crevices of the leaves, in a quiescent, 

 invisible and living state for a prolonged period. The only conditions that 

 could be inimical to these, the infective forms, would be atmospheric conditions 

 Effect of f marked severity, possibly a prolonged frost or a prolonged drought, 

 or destruction of the infected heather by fire or cutting. The effect 

 of extreme cold has been tested by subjecting the metamorphosed larvae to 

 freezing in the cold storage rooms at the Albert Dock for a period of a week. 

 On being thawed out of the solid block of ice it has been found that they 

 quickly regained their activity. Exposure to slow drying, on the other 

 hand, under experimental conditions, results in the death of the encysted larvae. 

 Effects of Death from lack of moisture must be continually taking place on the 

 drought. moorS) although there may often be, even at the hottest parts of the 

 day, an insensible transpiration from the growing plant, sufficient to maintain the 

 life of the larvae by preventing desiccation. Burning ^,nd cutting appear to be 

 the only practical means by which infected heather plants can be properly purged. 



To one more or less unaccustomed to the moors it is a matter of astonish- 

 ment to notice what might be described as the extraordinarily insanitary 

 condition of the Grouse's home. Nearly every square yard of moorland shows 

 traces of faecal deposits, and forcibly directs attention to the fact that there 

 is an unnatural over-population of the moors. 



When one remembers that practically all Grouse are infected with 

 Trichostrongylus pergracitis, and that from every dropping thousands of 

 Relation of potential parasites normally emerge, it becomes evident that the 

 ^ greater the number of birds upon a given area, the greater in turn 

 is. mus ^ De the, i n f ec ting capacity of the moor. But on most moors 

 only a very small proportion of the heather is suitable for food for Grouse 

 at certain times of the year, 1 and as the Grouse is a very heavy feeder it 

 follows that the parts of the moor from which the food supply is derived are 

 just those likely to be the most heavily contaminated with droppings. 



The number of birds on a moor should be correlated, not with the size of 

 the moor but with the extent of the suitable food area thereon. The amount 



1 Vide chap. iv. p. 71. 



