It would seem of interest to compare the results observed with the myeloblast system with those of analogous studies by Prince (17) on cell growth and virus formation in the chicken chorio-allantoic membrane inoculated with the Rous sarcoma virus. Although the conditions of the respective studies were entirely different, the analyses have revealed some points of similarity in the behavior of the two systems. The data were obtained from figure 5 of Prince's report. In his studies, virus increase was recorded in terms of pock-forming units (infectious units of virus), and the rate of cell growth was determined as increase in dry weight of the virus-inoculated membrane. The line through the growth points in text-figure 7, in our report, was drawn by the method of least squares, and, with the constants cited in table 1, calculation was made of the theoretical relationship concerned with virus formation as indicated by the dash line.

Growth and liberation of virus by myeloblasts derived from normal bone marrow

Text-figure 6. Growth and liberation of virus by myeloblasts derived from normal bone marrow exposed to myeloblastosis virus in culture (expt. 10258). The analyses were made by use of equation 4 as in the experiment of text-figure 1 (see text).

In text-figure 7 it is seen that the experimental data, with respect to virus extractable from the growths in the membranes, correspond closely to the theoretical values in the period from 36 to 144 hours of study. It may be concluded, then, that in this period of activity, the rate of Rous sarcoma virus formation per increase in membrane mass per hour was constant.

Analyses of the data on Rous sarcoma virus

Text-figure 7. Analyses of the data on Rous sarcoma virus obtained by Prince (17) by application of equation 4. The constants used were those given in table 1.

Decrease in extractable virus was noted in the initial stage of 16 hours, after which a rapid increase ensued. The observed rate of increase of extractable virus in the period between 16 and 36 hours, in relation to increase in membrane weight, was less than the expected rate. This is contrary to the interpretation of Prince, who considered the rate of increase in this interval as greater than the increase occurring in the later periods of the experiment. Whether the deviation from the theoretical was real because of the complexities of participation of two types of tissues in tumor formation, or due to technical difficulties of measurement in the early stages of growth is not apparent. It can be seen, nevertheless, that, as observed with the myeloblast culture system, the rate of virus formation in relation to increase in the mass of tumor was constant through a large part of the study.