Quantitative Significance of Alicroorganisin.s in Nnlrilion 707 



TABLE 4 



Importance of Various Food Components in 

 Nutrition of Calanipeda Aqua- Dulcis (in Damp Weight) 



300 1200 ml bacteria 87,264,000 0.042 



phytoplankton 2,073,600 0.218 



differ strongly from those living under natural conditions and 

 their nutrient value is doubtful in a number of cases. Therefore 

 we used a different way to obtain bacterial food, which would 

 in its composition resemble as nearly as possible the natural food. 

 Microorganisms, intended to serve as the food for small crusta- 

 ceans, received the radioactive tracer from the cells of phyto- 

 plankton in process of its decomposition. The bacteria were 

 separated from phytoplankton by the aid of membrane filters. The 

 plankters were placed into experimental vessels and lived there 

 48 hours during which time they were fed exclusively on bac- 

 teria. In course of that period their bodies acquired the tracer 

 element which they firmly retained after the experiment had been 

 carried out (Table 5). The data presented do not elucidate the 

 balance characteristic of the process, but they establish tlie pres- 

 ence of the carbon tracer in the body of the filtrator, acquired 

 from the microorganisms, and pro\'e the assimilation of the latter. 

 It should be supposed that the results of the experiment can 

 be extended, and applied to other representatives of plankton. 

 There is no fundamental difference in composition of the food of 



T.-XBLE 5 



Changes in Radioactivity of the Bodies of Planktonic Crustacaea 

 Fed by Bacteria Containing Tracer Elements ('in amp/min^ 



Expt. Radioactivity of Small Radioactivity of 



Crustaceans (Copepods) Bacteria 



Initial Final Initial Final 



I 408 600 327 



II 553 394 117 



