COMPETITION FOR COMMON FOOD IN PROTOZOA 



101 



curves of growth of P. caudatum and P. aurelia shows that as regards 

 the number of individuals the level of the saturating population of 

 P. aurelia is considerably higher than that of P. caudatum. Never- 

 theless, the comparison of the volumes shows something completely- 

 different; in this respect P. aurelia only slightly surpasses P. cauda- 

 tum, accumulating at the expense of a certain definite level of food 

 resources a scarcely larger biomass. As will be shown further on, 

 the Osterhout salts medium is not quite favorable in its properties 



fM 



5»» 



> 



"6 Jeo- 



200- 



J "x> 



P. caudatum 



o-e- 



I i 



Oayt 



Fig. 21. The growth of the number of individuals and of the "volume" in 

 Paramecium caudatum and Paramecium aurelia cultivated separately on the 

 medium of Osterhout. From Gause ('34d). 



for the Paramecia, and this complicates the question as to the factors 

 limiting growth. On the one hand, the insufficiency of food plays 

 a part here which we can judge of by a direct observation of the cul- 

 tures : with a population in equilibrium the turbid bacterial medium 

 introduced daily becomes quite transparent after a certain time, as 

 the bacteria are entirely devoured by the Paramecia. However, ow- 

 ing to a comparatively high concentration of bacteria and a somewhat 

 unoptimal reaction of the medium a depressory action of certain 

 other influences plays also a role here. 



