Studies of the conditions necessary for maintenance of constant cell populations in vitro in the Mackaness type of culture chamber have indicated the importance of preliminary trypsinization of cells and the beneficial effect of 40 per cent rabbit serum in Tyrode's solution. Under these optimal conditions, uninfected suspensions of monocytes exhibited little change in cell numbers over a period of 40 to 72 hours.
Infection of monocytes with the virulent H37Rv strain of tubercle bacillus resulted in an early degeneration of a certain proportion of the cells cultivated in the presence of normal rabbit serum. This degeneration was apparent not only for cells of tuberculin-negative animals but also for those derived from tuberculin-positive animals.
The serum of animals vaccinated with BCG exerted a favorable effect upon the survival of monocytes infected with virulent tubercle bacilli. Treatment with this serum caused a delay in degeneration of infected normal cells (cells of tuberculin-negative rabbits) and a complete inhibition of degeneration of infected immune cells (cells of rabbits vaccinated with BCG).