44 S. O. MAST AND F. M. ROOT 



much less for as pressure was applied to the fiber the pararaecium 

 did not flatten and become wider as was expected, but the de- 

 pression formed by the fiber extended down either side making 

 it narrower at this region, so that the length of the fiber in con- 

 tact was at all times less than the diameter of the Paramecium 

 and it gradually decreased as the groove made by the fiber be- 

 came deeper until it was reduced nearly to zero before the 

 Paramecium was entirely divided. 



Now the larger the area of the fiber in contact, the srnaller will 

 be the value of the surface tension in our calculation. We shall, 

 however, make the present calculation on the basis of the maxi- 

 mum, and consider later the effect on the result of reduction due 

 to contraction. The average diameter for 35 specimens of 

 aurelia, the species on which the amebae fed, was found to be 

 0.0494- mm., nearly 0.05 mm. If we assume this to be the 

 maximum length of fiber in contact in the process of cleaving 

 Paramecium, the area in contact will equal (0.005 X 0.0023.) 

 sq. cm. This value may be substituted for ab in the equation 

 given above, and the pressure applied (9 mgm.) for P. Then R 

 in the equation will equal the radius of the Paramecium being cut 

 by the ameba. But this varies from 0.0025 cm. to nearly zero, 

 and the greatest pressure required does not occur until after the 

 constriction has proceeded far enough to bring the ectosarc of 

 opposite sides in contact, that is, not until the diameter of the 

 Paramecium has been reduced to about 0.001 cm. Assuming 

 this statement to be valid, R would equal 0.0005 cm. Now 

 substituting all of these values in the original equation : 



T (0.005 X 0.0023) ^ 9 X 0.0005 



9 = , 1 = = 391 grams 



0.0005 ' 0.005 X 0.0023 



per centimeter = 383.18 dynes per centimeter or the minimum 



tangential tension in the rim of the food-cup required to cleave 



the Paramecium on the basis of the first of the two methods to 



be considered. But in cutting the Paramecium with the glass 



fiber the maximum pressure was applied when the length of fiber 



in contact was several times reduced. It is therefore evident 



that the tangential tension required is greater than 383.18 dynes 



per centimeter. But in a cup,' if the constriction of the rim is 



