224 THE GROUSE IN HEALTH AND IN DISEASE 



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 appreci- 

 able. 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 evapora- 

 tion of some of the water, so that the culture acquires more 

 consistency. 



A larger amount of water appears to be necessary for the 

 growth of the young parasite previous to hatching than after- 

 wards. Indeed we shall see later that a certain amount of 

 consistence in the medium 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 to segment until the resulting cells are exceed- 

 ingly small. The mass becomes somewhat flattened, and a 

 slight dimple appears at one border of the oval disc (Fig. 21). 

 This is the first step towards the formation of the cylindrical 

 body of the young embryo. By the gradual deepening of this 

 dimple the egg mass acquires a tadpole-like appearance, the 

 anterior end being, thus early, easily distinguished from the 

 posterior end of the body. The anterior portion soon exhibits 

 a central depression, which indicates the commencing forma- 

 tion of the mouth (Fig. 22). As the lateral dimple continues 

 to deepen the body mass elongates to such an extent as to 

 become folded upon itself two or three times, in order to become 



