"GROUSE DISEASE" STRONGYLOSIS 229 



April 13. Completes his hypothetical third and fourth moults, thereafter 



become adult and sexually productive. 

 ,, 13. Pairs as soon as adult stage is reached. 

 ,, 14. Lays eggs in caeca. 

 ,, 15. Eggs pass out of Grouse. 



Thus the exact mode by which the worms attain to the most favourable 

 conditions for infecting the Grouse had been determined, for the young 

 growing tips of heather are those most sought after by the birds. It 

 remained to be seen whether the administration of these metamorphosed 

 encysted larvse to healthy Grouse would result in the actual production 

 of Trichostrongylosis. 



It is related elsewhere in the Report that the administration of eggs 

 and embryos of the Trichostrongylus pergracilis and of centrifugalised wash- 

 ings of heather from the moors to healthy uninfected Grouse had 

 given uniformly negative results. From the observations described mental 



J induction 



above the explanation of these failures becomes very evident. The of Tricho- 



strongylosis. 



eggs and embryos of the parasite require to undergo certain essential 

 developmental changes for a period of almost a fortnight's duration before 

 they acquire the power of infection when swallowed by Grouse. The forms 

 got from the heather were undoubtedly non - parasitic nematodes and their 

 young, for these bear a general resemblance to the unmetamorphosed embryos 

 of Trichostrongylus pergracilis many of them having a very similar type of 

 mouth capsule. Moreover, the embryos of Trichostrongylus pergracilis do not 

 acquire their migratory habit until they have become metamorphosed, and there- 

 fore do not ascend the heather until they have entirely lost their oral capsule. 



Until the above described experiments were successfully concluded the 

 characters of the metamorphosed larvse were quite unknown, and therefore 

 it was impossible that they should have been recognised in washings of 

 heather. 



Owing to the fact that the deliberate administration of Grouse faeces to 

 healthy Grouse for the purpose of scientific observation is considered to be 

 a form of vivisection (accidental infection occurs continually on the moors), 

 and owing to the desirability that the various experiments of this character 

 should be carried out by one member only of the Committee, the cultures were 

 handed over to Dr Wilson for the purpose of administration to hand-reared 

 Grouse at the Frimley experimental station. 



