Figure 1.

Progressive changes in the growth-enhancing or growth-inhibiting effects of media conditioned on normal CEF (NCM) and RSV-infected CEF (RCM). About 2 × 10⁶ CEF freshly dispersed from 10-day-old embryos attached to the surface of 100-mm Petri dishes and initiated proliferation, dividing on average about once a day. Half of the cultures were infected with 10⁶ focus-forming units of B-RSV in synthetic medium 199 with antibiotics plus 10% tryptose phosphate broth (TPB) and 2% CS, and the other half were kept as controls in the same medium. The medium was replaced daily from the third day forward with 199 plus 10% TPB, 4% CS, and 1% chicken serum. It was centrifuged to remove any floating cells and released virus. It was then mixed in stepwise decreasing ratios with fresh medium in a total of 5 ml as shown in the abscissa and used to support the growth of 10⁴ CEF seeded in 60-mm dishes. The values on the ordinate are 1/20th the total number of cells per culture. The horizontal broken line indicates the total number of cells seeded, i.e., 10⁴ cells. (Left) NCM. (Right) RCM. The daily intervals at which the medium was collected accompany the curves of cell counts at 6 days. The point furthest to the right represents the number of cells in fresh medium, and the points above and to its left represent enhancement by increasing parts of NCM or RCM in 5 ml total. Points below the broken horizontal line indicate toxicity of the RCM. [Modified with permission from ref. 22 (Copyright 1966, Elsevier).]