Growth requirements of the meningococcus

The meningococcus has been considered one of the more fastidi-ous microorganisms with respect to growth requirements. Mueller and Hinton (1941) have shown, however, that excellent growth of this organism, as well as of the gonococcus, may be obtained on an agar medium containing only "double strength" meat infusion, casein hydrolysate, and starch paste. The purpose of the present investigation was to determine the essential factors in these mixtures. EXPERIMENTAL The organism used for the experiments was a type I meningo-coccus, isolated from a case of meningitis in Halifax, Nova Scotia. After approximately three transplants outside the human body, the organisms were emulsified in skimmed milk, sealed in small glass tubes, and quickly frozen in alcohol and solid carbon dioxide. The tubes were kept in a dry ice refrigerator. A fresh tube was used each day, so that the culture used for inoculation could be kept as constant as possible. Experiments were carried out with liquid rather than solid media. The volume of medium in each tube for most of the ex-periments was 5 ml. The tubes were incubated in candle jars, in a slanted position. Slanting the tubes, to expose a maximum surface, was found to be very helpful. At first the organisms grow near the surface. Shaking the tubes after a few hours ' incubation will make the growth more diffuse, and is another useful ex-pedient. Use of an atmosphere containing carbon dioxide is quite important. For estimation of the amount of growth, an inexpensive home-made photoelectric turbidimeter was used. Because of error