Abstract
In experiments of Pneumococcus transformation, several media have been devised in an attempt to improve the reproducibility of results ever since the in vitro reaction was first carried out by Dawson (1931) . It has been recognized that the occurrence of the in vitro reaction requires some environmental factors, in addition to the nutrients necessary for the initiation and maintenance of cell growth (McCarty et al., 1946) . Rabbit serum or human serous fluids provided such factors in many cases (E-Taylor, 1949; Austrian, 1952) . Hotchkiss and E-Taylor (1951) pointed out that bovine albumin could substitute the factors. However even in the presence of these factors, a reproducible and stable result was not necessarily secured in the Pneumococcus transformation. In order to obtain a constant and regular result in this reaction, it will be necessary to supply a better qualified medium and appropriate factor (s) . At the same time, elucidation of the nature of such factor (s), if any, will be significant to an understanding of the mechanism of the transformation reaction.
During the course of experiments performed in our laboratory on Pneumococcus transformation from SM sensitive to resistant cells, using heart infusion Neopepton broth as a basic medium, it was found that an addition of albumin and of horse blood hemolysate gave good results, while irregular results were obtained with the addition of albumin only. The experiments performed to ascertain the nature of the substance (s) in the hemolysate will be presented below.
