BIOLOGICAL ASPECTS OP INTRACELLULAR STAGES OF VIRUS GROWTH 137 



In selecting studies of viral growth to quote in this section an attempt was 

 made to choose experiments in which either a one-step growth curve was 

 carried out or some other method was used for restricting the viral growth to 

 a single cycle of multiplication. For herpes simplex and vaccinia viruses, 

 however, this has not been possible and values quoted for the rate of 

 growth and yield of these viruses are subject to the qualification that growth 

 of virus is accompanied by spread of newly formed virus to fresh cells with 

 secondary and later cycles of virus growth. 



E. Herpes Simplex Virus 



Scott et at. (1953) studied the growth of herpes virus on the chick chorion. 

 After a lag period of 6 hours the virus increased exponentially until about 

 16-18 hours, when a plateau was reached; this was followed by another slow 

 rise from 24 to 48 hours. The smaller the inoculum the longer was the lag 

 period but the rate of viral increase was independent of the size of the 

 inoculum, being about one log 10 every 2 hours. During the period of rise of 

 infectivity in the membranes there was a parallel rise of infectivity in fluid 

 washings (i.e., extra-cellular virus), but the titer in the washings was about 1 

 log 10 less than in the membrane. At 24-48 hours the titer in the washings was 

 about the same as that in the membranes. The results quoted by Wildy (1954) 

 follow closely those of Scott et al. After a lag period of about 6-8 hours there 

 was an exponential increase of cell-associated virus with an increase of about 

 3 log 10 over a period of about 10 hours; again the extracellular virus lagged 

 considerably behind the cell-associated virus. The presence of "steps" in the 

 growth curve, as suggested by Wildy, is not very clearly defined. 



F. Vaccinia Virus 



Briody and Stannard (1951) measured growth curves of vaccinia virus on 

 the chick chorioallantoic membrane. They thought that steplike increases in 

 virus activity occurred at 8 and 16 hours after infection, but the findings were 

 not consistent or in line with those of other workers. Anderson (1954), 

 working with the same system, noted a steady decrease in the amount of 

 recoverable virus up to the 9th hour. Thereafter, the amount of virus in the 

 membrane increased exponentially at a rate of about one log, every 4 hours. 

 Overman and Tamm (1957) studied the development of vaccinia virus grown 

 in pieces of chick chorioallantoic membrane in vitro. After a lag period of 

 about 8 hours the virus increased at a nearly exponential rate until the 48th 

 hour. However, in this system the growth of virus was much slower than when 

 virus was grown in vivo and the increase was only about 2 log 10 over the 

 40-hour period. The maximal virus yield in the membranes occurred at 3 days. 

 The titer of virus in the medium was always much less than that in the 



