Chemical Inblbifhn of Viruses 153 



Virus disease is dependent on virus reproduction in the 

 sense that, in the absence of reproduction, disease does not 

 develop. Reproduction of a virus does not always lead to 

 disease, however, and some viruses multiply extensively in 

 certain tissues without causing demonstrable abnor- 

 malities. There is some evidence that the relationship be- 

 tween the extent of reproduction and the amount of disease 

 is quantitative. With influenza virus or pneumonia virus 

 infections of the respiratory tract in mice, it is feasible to 

 compute how much pneumonia will develop by direct 

 calculation from the concentration of virus in the lung and 

 the time after inoculation (22, 29). 



If this relationship has wide validity, a possible means 

 for the control of virus disease opens before us. In theory, 

 inhibition of virus reproduction might be expected to re- 

 sult in less extensive disease. This conjecture has not yet 

 been tested adequately. But the evidence so far obtained 

 with one respiratory virus infection in mice, that is, 

 pneumonia virus of mice, is in accord with the idea. When 

 a chemical substance, in this case a bacterial polysaccharide, 

 is introduced into the respiratory tract, the greater the de- 

 gree of inhibition in virus reproduction, the smaller is the 

 amount of pneumonia that develops (23). Moreover, the 

 quantitative relationship between virus concentration, ex- 

 tent of lung lesion, and time is identical with that found 

 in the uninhibited virus infection (29). The amount of 

 pneumonia that will develop can be computed from the 

 other two variables. 



At first glance, such a result appears to be similar in 

 many features to that found when an antimicrobial agent 

 is employed in a bacterial infection. Bacterial growth is re- 

 tarded or stopped, and the disease is modified. In the ex- 

 ample just described there is, however, a distinguishing 

 feature that may be important. The substance used to in- 

 hibit virus reproduction has no effect upon extracellular 

 virus particles and does not prevent their adsorption by 



