" GROUSE DISEASE " STRONG YLOSIS 223 



found within the body of the Grouse must therefore have 

 actually entered it from the outside. We shall see later that 

 this explains the apparent anomaly that whereas practically 

 all Grouse are infected with Trichostrongylus only some suffer 

 from the disease. The egg, when newly passed, measures 

 0*075 mm. by 0*046 mm. and contains a morula, composed 

 of about sixty-four cells. 



If a freshly passed csecal dropping be isolated and kept Develop- 

 uncontaminated no further development will take place in the e gg outside 

 ova contained in it. A fungus will gradually grow upon it, thebod y- 

 and owing to this and bacterial contamination the eggs eventually 

 die. If the dropping be exposed to the drying influence of 

 sun and wind, as on the moors during summer, it becomes caked 

 and dry, and the eggs die. If, on the other hand, a csecal 

 dropping be spread out in such a way as to admit of the whole 

 becoming oxygenated by the atmosphere, and it be also slightly 

 moistened, development will proceed, its rapidity increasing 

 with the temperature. 



For the experimental study of the extra-corporeal develop- Cultural 

 ment the following method was found most reliable. Petri 

 dishes, as used in bacteriological research, of a diameter of 

 about 4 inches, were employed in pairs. Into the upper 

 dish was placed a closely fitting piece of thick blotting paper, 

 which was thoroughly moistened with water. The inside of 

 the lower dish was smeared uniformly with a very thin layer of 

 csecal dropping or csecal content taken direct from a dead bird. 

 Several drops of water were then added and mixed into the 

 viscid layer by means of a glass microscopical slide so as to 

 produce a glairy mixture that would but slowly slide off the 

 Petri dish when it was held almost upright. The layer of 

 fseces should be sufficiently thin to allow of an examination 

 under the microscope with a two-thirds inch lens. The upper 

 Petri dish was then placed over the lower dish, forming a close 

 chamber, the atmosphere of which quickly became saturated 

 with water vapour. From time to time the Petri dish was opened 

 and a small quantity of fseces removed on a platinum wire for 



