120 ALICK ISAACS 



However, in spite of the absence of demonstrable virus, addition of beef embryo 

 extract caused an immediate and rapid production of large amounts of virus. 



A variation of these techniques occurs in the experiments of Girardi et al. 

 (1952) on the recovery of meningopneumonitis virus during the lag period, 

 and similar methods were used later by Sanders (1953), Anderson (1954), and 

 Wildy (1954) in studies with encephalomyocarditis, vaccinia virus, and 

 herpes viruses. The principle of the method is that a piece of tissue is removed 

 during the lag period, part is homogenized and tested directly for its virus 

 content, while an aliquot is cultured in vitro and then tested for its viral 

 content. The object of the technique is to refine the experiments on recovery 

 of virus during the lag period by removing a piece of tissue and stopping 

 further virus absorption or spread of virus from neighboring cells or tissues. 

 The method has given recoveries of virus in the homogenized tissue as 

 compared with the cultured tissue of roughly 1 % for meningopneumonitis, 

 7 % for vaccinia (Anderson, 1954) and 10 % for herpes simplex (Wildy, 1954). 



It is difficult to summarize these varied studies on the recovery of different 

 viruses during the lag period. In many, there is not sufficient information to 

 allow us to estimate what proportion of the virus absorbed by the cells 

 became undetectable, but in those studies which allow us to estimate the 

 recovery, it is clear that, as a general rule, a large proportion of the virus 

 absorbed loses its infectivity shortly after entering the cells. Taking the re- 

 covery of less than 1 % found for bacteriophages as a standard, and making a 

 few assumptions about the experimental data, it appears that losses in 

 infectivity of about this order of magnitude, or slightly less, have been 

 described for western equine encephalitis, encephalomyocarditis, influenza, 

 fowl plague, Newcastle disease, Rous sarcoma, meningopneumonitis, and 

 psittacosis viruses. For herpes simplex the recoveries reported by Gostling 

 and Bedson and by Wildy may be about 10-20 %; for vaccinia virus, 

 recoveries of between 7 and 90 % have been reported by different investigators. 

 Leaving vaccinia and herpes aside temporarily, these large losses in virus 

 infectivity might be thought of as due to breakdown of the virus after entering 

 the cells or to the fact that the infectivity of animal viruses is often a very 

 labile property which might be unable to withstand the coarse methods of 

 extraction needed to prepare infected cell suspensions. If the latter explanation 

 were correct, it might be possible to show the presence of intact virus 

 during the lag period by testing for a more stable viral property, such as its 

 antigenic behavior. 



B. Attempts to Demonstrate Virus during the Lag Period by Its Antigenic 



Properties 



Most attempts to detect virus during the lag period by its antigenic 

 behavior have been carried out with the influenza virus hemagglutinin. 



