Studies on a Marine Parasitic Ciliate 369 



were not extended beyond one week of incubation. It was also 

 found that its infectivity withstood osmotic pressures in the 

 range of 320 mOsM to 1245 mOsM. 



A. Exposure to Virus of Carnivoroushj Feeding CiUates. Well 

 developed monolayer cultures were infected with poliovirus for 

 a period long enough to allow virus adsorption and multiplication, 

 but not gi"oss lysis of cells. This part of the experiment was 

 carried out at 37 C. After all supernate virus had been carefully 

 washed out, the infected cultures were divided in three groups. 

 One set was frozen at minus 20° C at this point of the experiment 

 in order to find out in a later titration the actual amount of virus 

 present at time. The second set was incubated at 30 C and 

 35 C in order to follow up the production of virus under the 

 experimental conditions. To the third set a known number of cili- 

 ates were added. The same numbers of ciliates were suspended 

 in comparable volumes of maintenance medium and also incu- 

 bated. The two latter groups of cultures represented a comparison 

 of ciliates in feeding and in starving condition. Supporting ex- 

 periments had shown that the presence of poliovirus in feeder 

 cells did not influence the growth rate of tlie ciliates. The ciliate 

 inoculum had to be large to guarantee a fast destruction of KB 

 cells so that they would not be able to produce considerable 

 amounts of virus during the experiment. At chosen time intervals 

 sister cultures of the three experimental sets of tubes were re- 

 moved from the incubator. The cilates were counted and the 

 specimens were frozen at minus 20 C for a later virus assay. 



B. In similarily designed experiments, tissue cultures of 

 grunt fin cells (Haemulon flavolineatum) were used as food 

 supply. In this case we know that the feeder cells are not able 

 to produce any virus above tlie offered seed dosage which is 

 suspended in Eagle's maintenance medium. We compared in 

 this system the effects on poliovirus of \'igorously feeding ciliates 

 and of starving ciliates. 



EXPERIMENTAL RESULTS 



Life Cycle Studies 



Twent\- clones were isolated in mammalian feeder cultures 

 of the KB line. In fifteen clones a sexual reaction of the selfing 



