Inhibition of the multiplication of PVM by the capsular polysaccharide of Friedländer bacillus, type B, is associated with restriction in the development of pneumonia induced with the virus in the mouse lung. The extent of the pneumonic process appears to be a function of the degree of viral multiplication; the greater the inhibition of multiplication, the less extensive is the pneumonia and the more probable is the recovery of animals treated with the polysaccharide. Effective therapy of pneumonia induced in mice with PVM is obtained with a single injection of 0.02 mg. of the substance given intranasally either 2 or 3 days after inoculation. Under appropriate conditions, treated animals recover completely from a viral infection which is, in control animals, uniformly fatal.

The polysaccharide produces inhibition if given in the first two-thirds of the latent period of the multiplication cycle, i.e., within 10 hours, but is ineffective when given at 12 hours or later. However, the second cycle and subsequent cycles are inhibited irrespective of the time the substance is injected during the first cycle of multiplication. The findings are discussed in relation to a theory regarding the mechanism of action of the polysaccharide.

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