INACTIVATION OF VIRUSES 417 



of inactivation, very little can at present be said. Most probably the effect 

 is mainly indirect, a "spontaneous" inactivation of the labile nucleic acid 

 after destruction of the protective coat. 



H. Miscellaneous Agents 



Some heavy metals were reported to inactivate viruses. Thus, inorganic 

 mercury is virucidal, although higher concentrations than those needed for 

 bactericidal effects are usually required. Kassanis and Kleczkowski (1944), 

 studying the kinetics of inactivation of TMV by mercuric chloride, observed 

 little or no effect at pH below 6 in the presence of molar KCl or NaCl, or 

 of HgCla concentrations of 0.01 % or less. Under suitable experimental con- 

 ditions, infectivity at first disappeared rapidly, the process soon slowing 

 down and reaching near equilibrium in about 30 minutes. The virus could be 

 removed from the reaction mixture by lovv' -speed centrifugation, a fact sug- 

 gesting that reduction of solubihty and precipitation play a significant part 

 in the process. 



Several authors reported at least partial reactivation after treatment with 

 HgS, thioglycoUate, or other — SH containing substances (Kreuger and 

 Baldwin, 1934; Stanley, 1935; Perez et al, 1949; Sinkovics and Markos, 1956). 

 Sinkovics (1956) presented data on influenza virus, exposed to HgClg for 

 different periods of time and titrated for infectivity before and after treat- 

 ment with HgS. His results are not inconsistent with the assumption of a 

 reversible surface reaction as the primary effect, followed by a more slowly 

 progressing, apparently irreversible process. Since the interior of the host 

 cell ought to provide good conditions for a reversion of the first stage, the 

 loss of infectivity in this stage has to be explained either by failure of the cell 

 to incorporate the virus, i.e., loss of avidity, or else by a toxic effect upon the 

 cell of the mercury -laden virus. The nature of the second irreversible reaction 

 is unknown. Of organic mercuric compounds, Merthiolate is of interest as a 

 widely used bacteriostatic and bactericidal agent. It has generally been found 

 to possess little or no virucidal activity. The stabihty of this substance does 

 not seem to be absolute. Whether the slow inactivation observed with certain 

 viruses is due to the organic comj^ound or to traces of inorganic mercury has 

 to be checked. 



Silver appears to act in much the same way as mercury, i.e., by precipita- 

 tion of the virus. Stanley (1935) obtained reactivation of silver-inactivated 

 TMV simply by dialysis. The "ohgodynamic" effect of silver ions, forming the 

 basic principle in certain methods for purification of drinking water, does not 

 seem to work on water-borne viruses. At least in the wTiter's laboratory, no 

 inactivation of poHovirus was observed even at silver ion concentrations of 

 4000 [jLg per liter. 



