OBSERVATIONS ON FEEDING OF AMEBA 45 



due to surface tension, it is only the difference between the sur- 

 face tension at the rim and elsewhere that can be effective. If 

 the paramecia then were actually cut by the contraction ofthe 

 rim of a food-cup due to the action of surface tension, there must 

 have been a difference in the surface tension of the rim of the 

 cup and that of other regions of the ameba equivalent to more 

 than 383.18 dynes per centimeter; and to make this difference 

 possible the surface tension of ameba must have been much 

 larger. 



If the cutting of Paramecium by ameba occurred in accord 

 with the second method mentioned above, that is, by the ap- 

 proach of the distal ends of two pseudopods, as the bulk of the 

 evidence seems to indicate, and if the cutting quality of the pseu- 

 dopods was the same as that of the glass fiber, then the pressure 

 exerted by each of the pseudopods must have been approximately 

 equal to 9 mgm. Since the pseudopods and the glass fiber were 

 nearly all of the same size their cutting quality was probably 

 practically the same. We may, therefore, assume that the pres- 

 sure exerted by them was, if the paiamecia were cut in this way, 

 9 mgm. 



If this pressure was the result of the action of surface tension 

 it must have been due to a reduction of the tension at the end of 

 the pseudopods equal to 9 mgm., and the width of the surface 

 involved must have been equal to the circumference of the pseudo- 

 pods. These were approximately 0.025 mm. in diameter having 

 a circumference of 0.078+ mm. The difference in surface ten- 

 sion between the end and the base of the pseudopods must there- 

 fore, if our postulates are valid, have been 9 mgm. or 8.72 dynes 

 per 0.078+ mm., which equals 1118+ dynes per centimeter; and 

 to produce this difference the surface tension of the ameba must 

 have been much higher. Consequently to cut a Paramecium in 

 two in accord with this method a much higher surface tension is 

 required than to cut it in accord with the first method. 



The process in question would, therefore, require, at the very 

 least, a surface tension considerably higher than 383 dynes per 

 centimeter and in all probability it would require a surface ten- 

 sion higher than 1118 dynes per centimeter, that is, practically 



