"GROUSE DISEASE" STRONGYLOSIS 231 



development. The first is completed prior to metamorphosis 

 while the larva is free-living ; the second, subsequent thereto, is 

 not completed until after the larva has entered the bird. 



So much then for artificial experiments. 



The following details of an experiment made during August 

 1909 serve to illustrate what actually becomes of the hatched 

 worms under natural conditions upon the moors. A culture 

 made in the manner described above was taken to a small village, 

 on the coast of the Bay of Cardigan, where no Grouse lived 

 or had been known to exist for many years. Two or three 

 small plants of hill heather were detached uninjured from 

 crevices in rocks. These were planted in a Petri dish, and the 

 dish was half filled with water so as to cover the roots. The 

 plants were then set aside. A week later they were found to 

 have survived the transplantation, and to have commenced to 

 grow under the new conditions. As the weather was showery 

 the plants and dishes were left out in the open, and for two or 

 three days in succession the raindrops hanging from the tips 

 of the heather were microscopically examined. They were 

 found to be almost free of life. On one occasion, however, 

 a small free -living nematode was found. Although slightly 

 resembling the larvae of Trichostrongylus pergracilis it was 

 readily distinguished from them by its microscopical characters. 



Immediately after one of these periodical examinations, 

 the culture of Trichostrongylus pergracilis, in which the majority 

 of the larvae had just undergone metamorphosis, was poured 

 into the water round the roots of one of the experimental plants. 

 The plant was left out in a typical " Scotch mist " for a couple 

 of hours. At the end of that time raindrops were again taken 

 from the highest tips of the heather, which were about 3| inches 

 above the surface of the water, and they were found to be liter- 

 ally swarming with the actively wriggling metamorphosed larvae 

 of Trichostrongylus pergracilis. These larvae had ascended the 

 wet stems and leaves of heather against the current of water 

 that was trickling down towards the roots. Their intense 

 activity was doubtless due to the large amount of oxygen 



