CHAPTER III 

 THE ACTIVITY OF VIRUS PARTICLES 



1. The Difference in Phage Activity due to the Cultivating 

 Condition of Host Bacteria 



The demonstration of active phage is usually achieved by using 

 an agar plate on which a proper dilution of phage-containing filtrate is 

 spread with the host bacteria. When active phage particles are pre- 

 sent in the filtrate, there will appear on the agar plate a number of 

 small circular areas of clearing in which no bacterial growth occurs. 

 These areas are called plaques. A plaque is regarded as produced by 

 a single phage particle which affects surrounding bacteria to cause the 

 lysis, and therefore the number of active particles can be estimated by 

 counting the number of plaques produced by a given quantity of the 

 phage-containing solution. 



As mentioned already, the protoplasm protein particles liberated 

 from the bacterial cells which have been affected by a phage appear to 

 be able to act as the virus. However, some of the particles seem to 

 act as such under appropriate conditions only ; if all the particles could 

 exhibit the phage action, it would occur only in extremely rare occa- 

 sions. 



It was found by Ohashi (43) that the ratio of the number of 

 particles able to act as active phage on an agar plate to that capable 

 of multiplying in a broth varies over a wide range with the filtrate 

 examined. He distributed a given quantity of a diluted phage filtrate, 

 in which one or less particle can be contained, into 20 tubes containing 

 bacterial broth suspension, and incubated them for a certain period of 

 time. From the number of the tubes, in which the phage multiplica- 

 tion failed to occur, and that of the total, he calculated statistically the 

 number of the active particles present. The number of active particles 

 thus calculated, however, never agreed with that estimated by counting 

 the number of the plaques produced on the agar plate on which a cer- 

 tain volume of the same filtrate has been spread with the bacteria. 



Ohashi examined about 40 different filtrates and found that the 

 ratio, so far as the examined filtrates were concerned, could vary from 

 about 0.1 to 3,000. This ratio was inclined in the majority of cases to 

 be smaller than 1.0, with about 80 per cent of the total samples the ratio 

 being found to be smaller than 1.0, indicating that the phage particles. 



