BIOLOGICAL ASPECTS OF INTRACELLULAR STAGES OF VIRUS GROWTH 125 



These experiments making use of antiserum, repeated washing, and RDE 

 have not always given unequivocal answers but, in general, it seems that in 

 nearly all the cases investigated most of the virus recoverable from cells 

 during the lag period is extracellular and can be removed by one or other of 

 these methods. Nevertheless, it has always been found too that a very small 

 fraction of the virus taken up by the cells can be detected in the lag period 

 and is not completely removed by antiserum, washing, or RDE. This virus is 

 therefore assumed to be intracellular, and, depending on our point of view, 

 we may regard it (hi experiments in which isolated cell suspensions were not 

 used) as the parent of the new virus yield which will remain infective through- 

 out the lag period, or as virus which is about to enter into an eclipse period, or 

 as adventitious virus of no significance in the multiplication cycle. Quantita- 

 tive considerations, however, make the first explanation untenable for many 

 of the above viruses. Thus, if we assume as average figures for influenza and 

 fowl plague viruses that 0.1 % of the virus taken up can be detected as 

 intracellular virus during the lag period, we are obliged to conclude that only 

 1 out of every 1000 infective virus particles taken up by the cell survives to 

 multiply, while the remaining 999 perish. But there is good evidence from 

 electron microscopic counts and indirect counting methods that infection with 

 these viruses can be initiated by 10 virus particles (Isaacs, 1957). When we 

 consider, too, the results of Hoyle and Frisch-Niggemeyer (1955) on labeled 

 influenza virus, it seems justifiable to conclude that on entering the cells the 

 majority of influenza virus particles become changed into material which 

 is either smaller or less dense than the original virus and which lacks 

 infectivity and many of the other properties of the virus; and that this change 

 may well be analogous to the eclipse phase of bacteriophages and cannot be 

 explained other than as a stage in the life cycle of the virus. 



At the moment we cannot say what is the significance of virus which is not 

 neutralizable by serum but is recovered during the lag period. 



With other viruses, the recovery during the lag period is almost as low as 

 that found for bacteriophages, but one cannot yet be certain that this is a 

 true eclipse. The findings with herpes simplex virus are conflicting. Wildy 

 (1954), Yoshino and Taniguchi (1956), and Stoker and Ross (1958) favor the 

 idea of an eclipse phase while Gostling and Bedson (1956) think it is not 

 proved; the same conclusion was reached by Maitland and co-workers for 

 vaccinia virus. Indeed, Maitland and Magrath (1957) report that a decline in 

 infectivity of vaccinia virus paralleling that which occurred in experiments 

 with intact chorioallantoic membrane was found when the virus was adsorbed 

 to membranes which had been heated at 56°C. for 20 minutes, a procedure 

 which destroyed the ability of the membranes to support virus multiplication. 

 The evidence cited for vaccinia and herpes simplex viruses seems therefore to 

 be insufficient at the moment to decide definitely in favor of or against an 



