Abstract
By labeling with isotope S35 it is shown that lysates obtained by growing phage T4r on strain B of Escherichia coli contain, in addition to finished phage, non-infective particles containing sulfur. These particles adsorb on bacteria and precipitate with A-T4 serum in a way similar to finished phage. They are somewhat lighter, however, and have no appreciable killing effect on bacteria. Previous expts. with P32 show that they do not contain nucleic acid.