220 THE GKOUSE IN HEALTH AND IN DISEASE 



oxygenated by the atmosphere, and it be also slightly moistened, development 

 will proceed, its rapidity increasing with the temperature. 

 Cultural ^'^^ ^^^ experimental study of the extra-corporeal development the 



methods, 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 ceecal 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 fceces 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 microscopical examination, or the lower part was placed upon the 

 stage of the microscope and directly observed. 



A similar method, and one which permitted the study of the various stages 

 of development in a small number of eggs, was the use of hanging drop dishes. 



If the former of these two methods has been adopted, in the course of twelve 

 hours the colour of the culture in the Petri dishes should have changed from a 

 greenish yellow to a reddish brown, and a sickly sweetish odour, similar to that 

 found in lactic acid fermentation, should have become distinctly appreciable. 

 Otherwise experience teaches that putrefactive processes will almost certainly 

 set in and lead to the destruction of the eggs and worms in the culture. After 

 the eggs have hatched, and when minute worms are seen wriggling through the 

 culture, it will be found advantageous to leave the Petri dish open for several 

 hours in order to allow of the evaporation of some of the water, and the culture 

 to acquire more consistency. 



A larger amount of water appears to be necessary for the growth of the 

 young parasite previous to hatching than afterwards. Indeed we shall see 

 later that a certain amount of consistence appears to be absolutely necessary 

 for the full growth of the young worm. 



In the culture made by the above method the egg mass continues rapidly 



