126 BRUCE D. REYNOLDS. 



III. IDENTICAL ENVIRONMENTS. 



When the experiments involving similar environments had 

 been completed, and before the experiments described in section 

 II had been performed, it seemed that the inability of an organism 

 to fuse with a protoplasmic fragment which had been severed 

 from a related individual was due to inherited physiological 

 variations. However, it was found, as shown in section II, that 

 by employing different environments the negative state was 

 reached in a much shorter time than was the case when the con- 

 ditions were unaltered. These results indicate either (i) that 

 the different environments have brought about heritable physio- 

 logical changes which influence the character of the reactions, 

 or (2) that the different environments have brought about tem- 

 porary physiological changes which do not persist after the organ- 

 isms are returned to identical surroundings. In other words: 

 the so-called "similar" environments may have, in reality, been 

 different. As Jennings ('16) pointed out, and Hargitt and Fray 

 ('17) and Phillips ('22) have shown by feeding Paramecia on pure 

 cultures of bacteria, food is an important factor in bringing about 

 modifications. There seems to be no doubt that certain forms of 

 bacteria prevail in one concavity while in an adjoining concavity 

 the flora may be entirely different. The Arcellce in hay infusion 

 cultures subsist principally on the bacteria by which they are 

 surrounded ; therefore, one should not be surprised if physiological 

 differences are exhibited between organisms kept in different 

 containers. 



Several methods might be employed in determining whether or 

 not the bacterial flora available to the organisms of two contrast- 

 ing lines are similar: 



1. By making cultures of the medium in which they are living, 

 and determining the kinds and relative proportions of bacteria 

 present through the use of differential culture media. However, 

 since little is known about hay infusion bacteria, this would be a 

 difficult undertaking. 



2. By isolating a pure strain of suitable bacteria and feeding 

 them to the organisms under aseptic conditions. 



3. (a) By frequently transferring small quantities <>f tlu- 

 medium from one concavity to the other, and (b) by placing both 



