"GROUSE DISEASE " STRONGYLOSIS 233 



April 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 deter- 

 mined, for the young growing tips of heather are those most sought 

 after by the birds. It remained to be seen whether the adminis- 

 tration of these metamorphosed encysted larvae to healthy Grouse 

 would result in the actual production of Strongylosis. 



It had been found that the administration of eggs and Experi- 

 embryos of the Trichostrongylus pergracilis and of centrifugalised Eduction 

 washings of heather from the moors to healthy uninfected ofStrongy- 

 Grouse had given uniformly negative results. From the 

 observations described above the explanation of these failures 

 becomes evident. The 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. Even the 

 administration of larvae was at first inconclusive, for the larvae 

 obtained from the heather in the earlier experiments were 

 undoubtedly those of non-parasitic nematodes, the young of 

 which 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 therefore 

 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 

 larvae were quite unknown, and therefore it was impossible 

 that they should have been recognised in washings of heather. 



The administration of the metamorphosed larvae was 

 carried out at the Committee's experimental station at Frimley 

 in Surrey. 



On June 19th, 1909, a culture of larvae which had just 

 undergone metamorphosis, and which were therefore in the 

 active migrating stage, was administered to an adult male bird 



