42 



S. O. MAST AND F. M. ROOT 



measured bj^ applying the end of the rod to the edge of a scale 

 pan and ascertaining the weight necessary to balance the rod 

 when bent through approximately 45 degrees. The results ob- 

 tained with two of the rods tested are briefly summarized in 

 table I. 



These results were obtained in tests made with paramecia from 

 two different cultures both of which contained aurelia and cauda- 

 tum. They are labeled A and B respectively. By referring to 

 the table it will be seen that the results obtained in the two sets 

 of tests which were separated by several days are essentially the 

 same; .and it will be seen that none of the 21 paramecia caught 

 under the weaker rod were cut in two, but that 19 of the 30 

 aurelia caught under the stronger rod were cut in two, while 11 

 were not entirely cleaved and that only one of the 17 caudatum 

 caught under this rod was divided. In applying the pressure the 

 hand was slowly raised and lowered so as to bring the rod to 

 bear fully upon the Paramecium. Some that could not be divided 

 in this way were divided by drawing the rod back and forth across 

 them but these were not recorded as cut. With the small rod, 

 however, we were unable to divide any even in this way no matter 

 how much the rod was bent, showing clearly that the pressure 

 necessary to cleave a Paramecium is unquestionably greater than 

 could be applied by means of this rod, that is, greater than 4.5 

 mgm. The fact that 11 out of 30 could not be divided with the 

 stronger rod without drawing the rod across them would seem to 

 'indicate that it is reasonable to accept the pressure produced by 



