PARAMECIUM IN PURE CULTURES OF BACTERIA 



445 



TABLE 7 



Growth of Paramecium aurelia in pure cultures of bacteria, in 0.1 per cent hay 

 infusion. Figures represent the number of divisions; cultures started on different 

 days. 1 dead. The last Jour lines of the table tvere alive at the end of the experiment 



strated but it is also clear that there must be produced by the 

 bacteria excretions which are toxic to the protozoa. The behav- 

 ior of Paramecium in some of these cultures is remarkable, for 

 example the animal lived in the pure culture of bacterium X 

 over a week, was active and apparently quite normal but in the 

 entire period had not undergone a single division. It would 

 appear that in so long a time Paramecium must have fed upon 

 the bacteria in order to remain alive, but the food while not 

 injurious seems not to be assimilated to any marked degree, or 

 growth would have taken place. In the culture of bacterium 

 IX Paramecium divided only once in the week it was living. 

 It is very obvious that the bacteria isolated from abnormal hay 

 infusions are not suitable food for Paramecium, but may in 

 some cases be distinctly injurious. - 



In the case of bacteria III, IV, V (isolated from normal hay 

 infusions), there is also no question as to their unsuitability as 

 food when used alone, since death of the protozoa occurred in 

 from a week to ten days. The first day or so in these cultures 



