INHIBITION OF MULTIPLICATION 205 



substance may act during the latent period of mumps virus (Ginsberg and 

 Horsfall, 1949), single-cycle multiplication experiments adequate to establish 

 this point could not be carried out. 



The polysaccharide not only inhibits the multiplication of PVM during the 

 latent period, but it acts as a chemotherapeutic agent in the strictest sense 

 and in the living mouse alters the course of infection with a small virus in 

 favor of the host (Ginsberg and Horsfall, 1951b). Under appropriate experi- 

 mental conditions, animals treated with a single injection of the substance, 

 after lung lesions have appeared, recover from a virus infection which is 

 uniformly fatal in control animals. 



2. 2, b-Dimeihylbenzimidazole (MB) 



This compound, designated MB, was used to initiate a systematic investiga- 

 tion of the inhibitory activity of derivatives of benzimidazoles relative to 

 their chemical structure (Tamm et ah, 1952). It inhibits the multiplication of 

 influenza A or B virus in the chorioallantoic membrane of the chick embryo 

 in vitro (Tamm et ah, 1952). 



In single-cycle multiplication experiments (Tamm et ah, 1953a; Tamm and 

 Tyrrell, 1954) the compound at 0.38 mg. per milliliter inhibited reproduction 

 of influenza B virus markedly when added at 1, 2, or 3 hours, and definite 

 inhibition was obtained even when it was added at 4 or 5 hours after inocula- 

 tion. It also inhibited the production of soluble complement-fixing antigen to 

 a similar extent throughout the same interval. The later the compound was 

 added during the latent period, the smaller was the inhibitory effect both on 

 virus multiplication and production of soluble antigen (Tamm and Tyrrell, 

 1954). 



The compound exerts an inhibitory effect throughout the latent period of 

 influenza B virus and for at least an hour after the end of the latent period. 

 The duration of processes inhibitable by the compound is therefore con- 

 siderably longer than those inhibitable by DRB (Tamm and Tyrrell, 1954), 

 which is described in a later section. 



MB does not inactivate the infectivity of influenza virus in vitro, and does 

 not decrease 2 consumption by the chorioallantoic membrane. It does not 

 cause an irreversible alteration in the host cells, for prolonged exposure to the 

 compound does not diminish the capacity to support virus multiplication 

 when the compound is removed (Tamm et ah, 1952). The biochemical basis 

 for the inhibition produced is not yet known. 



3. dl- Methoxinine 



This compound inhibits the multiplication of influenza A virus in the 

 chorioallantoic membrane of the chick embryo in vitro (Ackermann, 1951a). 

 In single-cycle multiplication experiments (Ackermann and Maassab, 1954b), 



