228 THE GROUSE IN HEALTH AND IN DISEASE 



Immediately after one of these periodical examinations, the culture of 

 Trichostrongylus pergracilis, in which the majority of the larvse had just under- 

 gone 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 3J inches above the surface 

 of the water, and they were found to be literally swarming with the 

 actively wriggling metamorphosed larvse of Trichostrongylus pergracilis. 

 These larvse 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 present 

 in the fresh rain. The plant was then taken from the Petri dish and 

 placed in a cardboard box, which was sealed down. A month later the 

 box was opened. The heather was found to be alive still and growing, 

 but very dry. The tips of the shoots from which the raindrops had been 

 taken were cut off and soaked in little watch glasses of fresh water, and 

 in the course of half an hour there wriggled out from the crevices of the 

 leaves of the heather a considerable number of larvae, showing at either end 

 the long collapsed parts of the sheath which as we have already seen 

 are characteristic of the larvse that have undergone drying under artificial 

 conditions. The intestine showed the characteristic refractile appearance 

 already noted. 



The following synopsis of the life-history of this parasite may be of interest 

 Synopsis as summarising the order and minimal duration of the various stages 

 history. in the life-cycle. 



April 1. Egg in morula stage passes out of Grouse. 



,, 3. Larva hatches out and lives in dropping or in moist earth. 



,, 5. First moult or ecdysis. 



,, 8. Metamorphosis, larva now in actively migrating form. 



,, 9 (or after). Larva ascends to tips of heather; if there is no mist,, 

 rain, or dew the ascent will be postponed. 



,, 10 (or after). Encystment or drying; this represents the first stage 

 of the second moult an indefinite interval may intervene 

 here. 



10. Larva swallowed by Grouse, and completes second moult. 

 11. Reaches ceeca of Grouse. 



