March 2, 1955
Dear Josh
Glad to hear from you and to know that you got some results with the filter and these seem to make sense. The intimacy of cellular association which seems to be required for the transmission of "F" is intriguing. It seems to be at least one step closer that what is involved in Kidney [ . . . ] induction, and thereby raises another little notch my doubts about infective transmission as a mechanism of embryonic induction.
I would be interested in knowing whether you found any difference in the frequency of "break through"  within the H and P filters. I am now convinced that there are real differences between these two both as to visual [ . . . ] by stain [ . . . ] and phage- positive materials, and passage of inductive effects. On the other hand, the two appear to be equally susceptible to "spotting," which I tentatively assume to be the result of [ . . . ] what is almost certainly protein and may be present  glycoprotein. I would expect that if cellular break through is a function of porosity it would be distinctly more frequent with A[? ] type filters.
We have plenty of the [ . . . ] filter materials on hand, so by all means keep what you have. Krahek[?] tells me they have somewhat improved their procedures, and I may ask him to make another batch of thin stuff sometime soon. If so you could certainly get in on it, thus avoiding the special fee[?] they charge for setting up.
Best,
Clifford