Abstract
It was reported 1 that mice could be infected by intraperitoneal inoculation with small numbers of virulent meningococci suspended in a solution of mucin. The mucin used in those original experiments was a commercial product which is prepared from hog's stomach and marketed for the treatment of gastric ulcer. The strains of meningococci employed had been freshly isolated from the spinal fluids of patients suffering from epidemic meningitis, and of these strains the 2 which proved lethal in highest dilution were those which had been obtained under conditions that permitted initiation of the experimental infection in the mouse most quickly after aspiration of the spinal fluid.
When work on this problem was resumed after several months, the minimal infecting inocula proved to be much larger than they had been in the preceding spring and summer. To explain this variation, attention was directed to the meningococci, the mice, and the mucin. In the case of each lay a possible source of our difficulty because the following changes had occurred:
1. Our cultures had been carried for a considerable length of time on artificial media without transfer to mice. Efforts to enhance the virulence by mouse passage were unavailing, and fresh strains of meningococci could not be secured because of the low incidence of epidemic meningitis in Chicago at the time.
2. Mice were difficult to obtain and came mostly from dealers who had not previously supplied us; presumably, therefore, from different stocks.
3. A new lot of mucin was being used as our initial supply had been exhausted. Several lots obtained from the laboratory which had furnished it and samples from the 2 other manufacturers who prepare mucin commercially were equally ineffective in facilitating experimental infection with small numbers of organisms.
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