This paper, which predated Griffith's' paper (No. 12833), demonstrated that the scrapie agent replicates without nucleic acids. Alper and colleagues irradiated scrapie infected mouse brain extracts with lethal ultraviolet rays at both 254-265 and 280-285 wavelengths, which would kill all viruses and bacteria then known, and inactivate or destroy nucleic acids. They did not draw the conclusion that the scapie agent must be associated with a protein, but that was the clear implication of their research. This paper was a catalyst for Griffith to develop the work published in No. 12833.

(Thanks to Juan Weiss for this reference and its interpretation.)