102 PROTISTS AND DISEASE 



are dealing with an obligatory parasite only a certain limited 

 number of stages are to be expected in such cultures. 



Considered as isolated phenomena the subjoined facts are 

 evidence of vitality in molluscum bodies : taken together 

 they either prove this vitality or they prove the microscope 

 to be useless for the study of protistic life. Personal practical 

 work of the simplest kind is required for any one to witness 

 the vital phenomena. 



I 



B 



FIG. 28. A METHOD OF WATER CULTURE. A, the material to be'cultivated 

 is heaped in the middle of a watch-glass and water, but not enough 

 to cover the material, has been added drop by drop ; - B, after teasing 

 in a drop of water on a slide, a particle or drop of the material in A 

 is covered and examined microscopically, then the preparation is 

 inverted over a watch-glass containing water and put between Petri 

 dishes for re-examination later. 



The culture must be kept at room temperature, because 

 incubation favours the growth of bacteria, which, when 

 abundant, kill the specific parasites. Occasionally a culture 

 apparently free from bacteria is obtained, but usually 

 bacteria are present ; in moderate number they do not 

 prevent vital changes from occurring. 



It is important to make clear drawings of objects at the 



