The cells used in this experiment were those derived from the same cultures described in the preceding section. On the 577th day of culture, the medium was changed to the mixture of equal parts of chicken serum and medium 199 supplemented with additional amounts oj B vitamins, including the high concentration of folic acid. The results observed during the study period between 645 and 675 days are shown in text-figure 5. Here it is seen that the pattern of cell proliferation and virus liberation observed with these cells derived from long-term culture under highly varied conditions is identical with that of cells freshly obtained from the bird. The rate of cell growth was exponential with a generation time of 7.4 days. With the use of the relations of equation 5 in the manner described for experiment 8759 and the mean constants given in table 1, the calculated dash line was derived as shown. As can be seen, the agreement between the calculated line and the experimental points is excellent. From this it can be concluded that the variations occurring in the liberation of virus by these cells under the different conditions prevailing before must have been related to deficiencies in the medium.

Cell growth and virus liberation in a later period

Text-figure 5. Cell growth and virus liberation in a later period, 645 to 675 days, of the same long-term culture established as shown in text-figure 3. Beginning on the 577th day, the culture medium was 50 percent chicken serum in medium 199 with added glucose and B vitamins and a concentration of folic acid of 0.4 g. per ml. of whole medium. The continuous line was drawn through the cell data by the method of least squares, and the dash line was constructed by application of equation 5.

Myeloblasts Derived By Treatment Of Normal Bone Marrow Cultures With Myeloblastosis Virus

In an earner report (5) there was described the proliferation of myeloblasts in cultures of normal bone marrow exposed to the myeloblastosis virus. The medium used in these studies was 50 percent chicken serum in medium 199 without B vitamin supplement. Analysis has been made here of the results of one of the experiments of the series, text-figure 1 of (5). Measurement of cell growth in that study was made not by cell count but on the basis of the number of cultures accumulating during the study period. The constants derived for cell growth and virus liberation are given in table 1. The data of the experiment are charted in text-figure 6.

Here it is evident that, from the time of the beginning of cell growth at 22 days, the rate of proliferation was constant with a generation time of 3.6 days. Again, as in the other types of experiments, the observed data on virus liberation conformed closely to the theoretical, represented by the dash fine derived by use of equation 4. The rate of virus liberation was 19.5 particles per cell per hour. In principle the behavior of the myeloblasts emanating from normal bone marrow exposed to virus in vitro was identical with that of myeloblasts from diseased birds established in culture.