Quantitative Signifuance of Microorganisms in Nulrition 705 



qiiaiititatix'c and weiglit analysis employed in our experiments 

 with the benthic forms was inapplieable in this case, for it was 

 impossible to produce sufficientK' fine preparations and weights. 

 The chosen method was based upon the principle of observing the 

 changes of concentration of cells used as food, in vessels con- 

 taining small planktonic crustaceans (Copepoda) with oar-like 

 swimming feet, Calanipeda (Kptd diilcis, taken in the Sea of Azov. 

 The mixture of cells of algae and bacteria dc\ eloped in flasks con- 

 taining phytoplankton, which is a nutriment similar to that under 

 natural conditions, was offered as food. In each variant of the ex- 

 periment, the numbers of both the bacterial and phytoplanktonic 

 cells were counted simultaneousK. This enabled us to compare 

 the consumption of the two kinds of food without prexiously plac- 

 ing the animals under conditions of forced feeding solely on bac- 

 terial cells. The duration of the experiment was shortened as much 

 as possible, so that the numerical \alues for ingested cells should 

 not be influenced by the reproduction of bacteria. At the same 

 time, the possibility of polluting the medium by undigested mi- 

 crobial cells was minimized. In the course of time that the small 

 crustaceans were in the experimental vessels, a decrease of con- 

 centration of the cells of the two food components was, as a rule, 

 observed. It became possible to determine, on these grounds, the 

 rate of filtration according to the formula proposed by Gauld 

 ( 6 ) . Having both the rate of absorption of food cells from a def- 

 inite volume of water by one animal in a unit of time and the 

 volume of water filtered in twenty-four hours, it is easy to calcu- 

 late the twenty-four hours consumption of food by one small crus- 

 tacean. 



The problem arose as to the definition of the optimum rate 

 of filtration. The rate of filtration is not a constant; it depends 

 upon a number of factors, of which the most important is the ini- 

 tial concentration of food cells (Fig. 2). Calculations were made 

 using food-cell concentration proper to the habitats of calani- 

 peda ( 10,{)00-20,00() cells ]ier 1 ml ) . The size of that rate of filtra- 

 tion fluctuated from 0.11 to 0.25 ml per hour. 



In order to compare the two kinds of food, i.e., algae and bac- 

 teria, we calculated the rate of consumption of cells by one small 

 crustacean in an hour. Those rates were respectively for ph\to- 



