OBSERVATIONS ON FEEDING OF AMEBA 43 



this rod as that necessary to cleave a majority of the animals, 

 and to conclude that amebae in cutting paramecia in two exert 

 a pressure as great as this. 



The pressure of this rod bent through 45 degrees equaled 

 approximately 9 mgm. as the following results show. With 9.2 

 mgm. in one pan the beam could not be brought to a level with 

 the rod applied to the other; with 8.8 mgm. the beam could be 

 brought to a level without bending the rod through quite 45 de- 

 grees; while with 9 mgm. the beam became practically level when 

 the rod was bent through 45 degrees. 



If now the cleaving of Paramecium by amebae in the process 

 of feeding is due to a change in surface tension at certain points, 

 what must the magnitude of this change be? The answer to this 

 question depends upon what actually occurs during the process, 

 that is, upon whether the paramecia are cut in two hj the con- 

 striction of the rim of a food-cup or by the approach of the distal 

 ends of two pseudopods. We were unable to ascertain from our 

 observations which of these two methods prevailed, but the bulk 

 of the evidence at hand favors the latter. Moreover, if a cup 

 was actually formed some factors aside from surface tension must 

 have been involved in its formation, for it is evident tha-t an invag- 

 ination is impossible in a body the form of which is dependent 

 solely upon surface tension. Let us however, assume a cup form- 

 ed and calculate the change in surface tension necessary to ac- 

 count for the cutting of the paramecia on the basis of both of 

 the methods in question. 



The surface tension required in case the cutting is due to the 

 constriction of a ring, e.g., the rim of a food-cup, can be calcu- 



T 

 lated from the following formula: P = — ab, in which P = in- 

 ward pressure, R = radius of ring, ab, = total area in square 

 centimeters involved in the pressure (P), and T = surface ten- 

 sion per centimeter. Now we know that to cut a Paramecium 

 it requires a pressure of approximately 9 mgm. on a glass fiber 

 0.023 mm. in diameter. The length of the fiber in contact with 

 the Paramecium during the process of cutting could not exceed 

 one-half of the circumference. It actually was continuously 



