COMPETITION FOR COMMON FOOD IN PROTOZOA 91 



and at the present level of our knowledge we will have to undertake a 

 detailed analysis of the most simple cases only. But the words of 

 Boltzmann compel us to turn our particular attention to those narrow 

 links in the conditions of our microcosm which constitute the real 

 objects of the competition. In the foregoing chapter we had to deal 

 with a competition of the yeast cells for the utilization of a certain 

 limited amount of energy in the test tube. The limit for the growth 

 of the biomass in these organisms was connected with the accumula- 

 tion of the waste product (alcohol), and this factor stopped the growth 

 before the exhaustion of the energetic resources of the microcosm. 

 As a result the entire process of competition could be expressed in 

 terms of the narrow link — alcohol production. Thus the situation 

 in these experiments was a peculiar one. 



In the present chapter we will try to approach the regularities 

 which, as Boltzmann supposed, are characteristic for the biosphere 

 as a whole. We will examine the struggle for existence in carefully 

 controlled populations of Protozoa. Here the growth will be limited 

 by an insufficiency of organic nutritive substances, a factor analogous 

 to an insufficiency of available energy. The second peculiarity is 

 that the energetical resources of the microcosm will be maintained 

 continuously at a certain fixed level in the course of the experiment. 

 This approaches somewhat to what exists in nature, where the level 

 of energy is maintained by the uninterrupted influx of solar energy. 

 As before we will be concerned in these experiments with the problem 

 in what proportion the energy of the microcosm will be distributed 

 between the populations of the two competing species. But besides 

 this first stage we shall be enabled to examine here the following 

 fundamental question: Will one species drive out the other after all 

 the available energy of the microcosm has been already taken hold off 

 And if so, will one species in these conditions drive the other one out 

 completely, or will a certain equilibrium become established between 

 them? 



(3) It has been already tried more than once to use Protozoa for the 

 study of the communities of organisms and their succession under 

 laboratory conditions. But as an ecologist has recently remarked, 

 the mere fact of a community set up in a laboratory dish does not 

 mean at all that it is simple. Interesting observations have been 

 made on the succession of communities of Protozoa in a hay infusion 

 by Woodruff ('12) Skadowsky ('15) and more recently by Eddy ('28). 



