52 



Regulation of Size in Unicellular Organisms 



individuals. During this shrinkage it is probable that 

 water alone was lost, whence the water content may be 

 regarded as relatively less in the small individuals. If, 

 instead, the shrinkage had been limited by the surface- 

 mass ratio of the body, then it would have been less in 

 the large animals. 



50 



840 



o> 

 o. 



.E30 



CD 



— 20 

 o 



> 



CQ 



4 



°0 1 2 3 4 5 6 7 



Relative original volumes of body 



Figure 23. Effect of solutions of sucrose upon the mean body volume of 

 Paramecium caudatum. Triangles, sucrose of 9 atmospheres osmotic pres- 

 sure; circles, sucrose of 10 atmospheres osmotic pressure. Broken line, 

 average linear correlation. The Paramecia measured were classified into 

 groups of 7 to 34 individuals according to their original body lengths (ab- 

 scissae) and the mean body volume after shrinkage is given in per cent of 

 the mean original volume of each group (ordinates). (Data of Fortner, '25). 



The relation of locomotion to size also involves the 

 relation of rate of sinking to size. As an example, 

 locomotion by cilia is limited by the number of cilia 

 that can operate on the surface, while the mass to be 

 moved is relatively larger than the surface in large 

 individuals. Ludwig ('28a) estimated the limitation 

 of size of Paramecium upon this basis. But there is 



