PARAMECIUM IN PURE CULTURES OF BACTERIA 441 



The preparation of the medium and its inoculation with known 

 bacteria was as follows: before the culture was started a large 

 number of tubes were filled with the 0.1 per cent hay infusion 

 and sterilized so the medium used throughout the experiment 

 would be the same. On each day one of these tubes (to be 

 used the next day) was inoculated with the desired kind of bac- 

 teria by transferring some on a sterile platinum loop from the 

 pure culture in an agar slant to the hay infusion. This transfer 

 was made in the usual way for such transfers in all bacteriologi- 

 cal work and, therefore, involved no contamination from the 

 air. By inoculating a tube of the infusion ahead of time the 

 bacteria got a good start, the medium when shaken would have 

 the bacteria v/ell distributed, and if any chance contamination 

 occurred when the Paramecium was shifted to the new medium 

 the contaminating organism would be only one in an enormous 

 number and would thus have little effect in modifying the diet 

 of Paramecium. 



From the above account we believe it is shown that we have 

 been able to devise a technic which is practical and successful. 

 It appears to us that every possible sort of check and control 

 has been applied to test the method and to determine the purity 

 of cultures, and the like. All these were worked out and per- 

 fected before the experiments later described were started so 

 that the preliminary cultures were not considered in the data 

 which follows. Furthermore in the transfers and manipulation 

 of cultures and media only one of us (Mr. Fray) took part, so 

 there can be no difference in the matter of skill and method of 

 preparation and handling. All this would seem, therefore, to 

 warrant us in the behef that our results, so far as they go, are 

 without error. 



Growth of Paramecium in Pure Cultures of Bacteria. The hay 

 infusion having been analyzed bacteriologically, the various ex- 

 periments already described having been completed, and an 

 effective and carefully controlled technic having been devised, 

 it was possible to start cultures of Paramecium in pure cultures 

 of known bacteria. Again let it be mentioned that all the 

 protozoa used were of a single pure strain, i.e., all were descend- 



