374 Marine Microbiology 



at time or on vims sui-vival after seven days of incubation. Even 

 the medium containing 100 per cent seawater, while showing 

 what appears to be a decrease in infectivity of 1 log at time 0, 

 failed to exert any consistent effect upon incubation. 



TABLE 3 



Infectivity of Polio Strain Mahoney Recovered After Incubation 

 Media of Various Salinities 



A very interesting fact evolved when poliovirus was given 

 to grunt fin cell monolayer cultures. No cytopathogenic changes 

 could be observed. When, however, the supernates were screened 

 for the presence of active virus, it was found that the infectivity 

 was lost within a shorter span of time than could be accounted 

 for by mere loss through incubation at 20 C. This "factor" 

 released by fish cells into the medium lost its effect gradually 

 with duration of incubation. The nature and specificity of tliis 

 interaction is unknown and is the subject of further studies by 

 our group. 



A very important support for our hypothesis that parasitic 

 ciliates act as vectors between fish seems to be the fact that 

 ciliates were not killed if exposed to poliovirus either in the 

 carnivorous or in the saprozooic feeding system. As long as the 

 chosen experimental set-up (nutrient supply and temperature) 

 guaranteed multiplication, we found comparable cell production 

 in the presence and in the absence of virus. The infectivity titles 

 suffered some loss in long extended experiments due to the incu- 

 bation effect but not in short term experiments. Unfortunately 

 ciliates did not stand up well to centrifugation. It was, there- 

 fore, difficult to separate them from the culture fluid. We have, 

 however, some evidence that virus was associated with the 



