VII THE MODE OF VIRUS MULTIPLICATION 91 



Usually the viability of bacteria is examined by plating on agar 

 and the bacteria incapable of forming colonies are regarded as having 

 no viability or being dead. This might be another main reason for 

 which the erroneous conclusion was reached. Cohen attributed the 

 rapid increase in the amount of both protein nitrogen and nucleic acid 

 in the bacterial culture infected with phage to the multiplication of 

 phage itself, but this may show nothing but the rapid growth of bac- 

 teria after the infection. 



Kozloff et al. in the above cited chemical studies of virus reproduc- 

 tion, stated that the percentage of the phage protein nitrogen derived 

 from the bacteria was inversely proportional to the time of incubation 

 and to the number of virus particles produced per bacterial cell. This 

 may only be a natural result, since the prolonged period of incubation 

 and increased number of virus particles per bacterial cell should be 

 accompanied by the increased number of newly developed bacterial 

 cells. They appeared to take into consideration only the bacteria 

 which had been present at the beginning to reach the erroneous con- 

 clusion. 



Such unreasonable conclusions seem, however, to be reached only 

 with phage. A study on the uptake of radioactive phosphorus by 

 influenza virus by Graham and McClelland (105) has shown that there 

 is no direct exchange between the virus and phosphorus. It has been 

 known for a long time that the increase of a plant virus is accom- 

 panied by a decrease in normal protein. For example, Wildman et al 

 (106) made electrophoretic analysis of cytoplasmic protein solutions 

 isolated from tobacco plants at different intervals after inoculation 

 with tobacco-mosaic virus, and found that a predominant normal por- 

 tion decreased as the virus protein increased by approximately the 

 same amounts, suggesting that the virus protein is synthesized at the 

 direct expense of the main protein component. 



In an experiment with P^^-labeled host bacteria, Putnam et al (107) 

 have reported that from 60 to 90 per cent of the phage P is derived 

 from bacterial nucleic acid, and concluded that bacterial nucleic acid 

 is the chief precursor of phage nucleic acid. It is remarkable that 

 even with phage and bacteria such rather reasonable conclusion was 

 reached, although the small portion of P had yet to be ascribed to 

 that contained in the culture media. 



According to Stent and Maaloe (108) oh the average 58 per cent of 

 the phosphorus is host derived in the first 15 per cent of the phage 

 particles formed, while the average over the total yield indicates 

 only 30 per cent of the phage phosphorus to the host derived. This 

 result again suggests the multiplication of the bacteria after the infec- 

 tion. Labaw (109) found that the amount of bacteriophage phosphorus 



