426 GEO. T. HARGITT AND WALTER W. FRAY 



negligible as a modifying factor in their experiment. In a further 

 attempt ('11 d) to so control the experimental factors as to deter- 

 mine whether rhythms in reproduction were due to environment 

 they still depended upon the chance inoculation of their media 

 by the transfer of the bacteria with the Paramecium at the time 

 of its isolation. Their behef that the variation in the bacterial 

 content was slight may have been true as to numbers of bacteria, 

 but it is probable that the kinds of bacteria may have been, or 

 come to be, decidedly different. In one cultiu*e, for example, 

 one kind of bacteria might have got the start and become the 

 predominant kind, while the predominant type in another cul- 

 ture would be different, and such difference might be significant. 

 Wliether it was ''unnecessary to attempt to 'sterilize' the para- 

 moecia and feed them on pure cultures of bacteria" they cer- 

 tainly could not determine without a trial. 



Other work done since this time on Paramecium has not added 

 anything so far as the nutritional factors are concerned. There- 

 fore, from this brief summary it is clear that not a single worker 

 has had any precise knowledge of the bacterial food of Para- 

 mecium in experimental work. Furthermore all have entirely 

 neglected the precaution insisted on by Jennings of making the 

 'bacteria the same,' save Jennings, himself. While it is not to 

 be expected that each worker would laboriously perform his 

 experiments under strict bacteriological methods, it is compara- 

 tively simple and easy to use a method like that of Jennings 

 to render the bacterial content of media as nearly the same as 

 possible. The data obtained by us will show that it is not 

 necessary to carry on all of this work with a strict bacterio- 

 logical technic. But it will be as clearly shown that there is the 

 necessity of securing a uniformity of bacteria in all cultures which 

 are to be compared, and also the desirability of excluding cer- 

 tain kinds of bacteria from the cultures. 



METHODS AND OBSERVATIONS 



Bacteriological analysis. Two main points are involved in a 

 bacteriological study of the hay infusion: 1) what bacteria are 

 normally present in a healthy hay infusion; 2) what forms 



