68 C. G. A. ROOS 



Fluid media offer no advantage over solid media and they 

 are of course not adaptable for isolation. Gelatin is not suit- 

 able because the meningococcus does not grow at low tempera- 

 tures. 



While many of these media, offer satisfactory conditions for 

 growth during a few generations, a fair proportion of strains 

 kept upon them suddenly fail to develop and in spite of persistent 

 effort cannot be resuscitated. Furthermore on all the above 

 mentioned media the cultures under ordinaiy conditions must 

 be transplanted at short intervals — not longer than two or three 

 days — ^and kept constantly in the incubator at 37.5°C. (Ex- 

 ceptional strains are found which are unusually hardy and seem 

 to require little more care than the common saprophytic bacteria.) 



With all the above culture media, those favoring the rapid 

 growth of the meningococcus at the same time result in rapid 

 ferment production and consequently rapid death of the culture. 



After innumerable trials we have found a medium which 

 permits of relatively slow growth of the meningococcus with 

 apparent suppression of ferment formation, thus resulting in 

 greater viability. This medium has been in use for about two 

 years and its superiority over the other media mentioned in the 

 literature for the maintenance of stock cultures of the menin- 

 gococcus seems to warrant its publication. This culture medium 

 is a modification of the potato-blood-agar used by Bordet and 

 Gengou for the isolation of B. pertussis. 



Preparation of medium 



1. Prepare potato extract as follows: 



a. Potato peeled, cut in small pieces and washed in running water 

 for about two hours, 100 grams. 



h. Water containing 4 per cent double distilled glycerine free from 

 acid, 200 cc. 



c. Mix and autoclave for forty minutes. 



d. Allow to stand over night and strain through cheese cloth. 



2, Make potato-extract-agar as follows : 



a. Mix in an Erlenmeyer flask: Potato extract, 50 cc; NaCl solution 

 0.65 per cent, 150 cc; agar 5 grams. 



