Diffusion of Influenza A Virus from Mouse Lung Material and Titration

In brief the technique (1) consists in placing a layer of solvent above a layer of solution containing the virus, allowing the latter to diffuse upwards for a few days, sampling at various heights, and determining the virus titer in the samples. The original virus concentration, expressed in lethal doses, or minimal infective doses, per inoculum, is Co, and C, is the concentration x centimeters above the initial boundary, at the end of the experiment. In order to determine the diffusion constant D, log C~/Co is plotted against x, and the theoretical curve is drawn which gives the most satisfactory fit. For x = 0, log C,/Co is always equal to -0.3. (This point, therefore, does not have to be determined by experiment; it is indicated on the charts as a half circle.) The diameter d of the virus particles may then be derived from the diffusion constant, the assumption being made that the diffusing particles are approximately spherical. In the experiments reported here, the virus concentration at the bottom of the diffusion cell was taken as Co. Sampling was done up to 1.2 or 1.3 era. above the initial boundary; above this level the fluid usually still contained a trace of virus, but too little for quantitative titration.