518 PATHOGENIC MICROORGANISMS 



growth, but, owing to acid formation, tends to cause a more rapid death 

 of the culture. In flasks of broth containing glucose one per cent, and 

 CaC0 3 one per cent, however, cultures have been kept alive for as 

 long as fourteen months (Hiss). On milk, growth takes place without 

 coagulation of the casein. Potatoes are not a favorable medium, 

 though growth occasionally takes place. 



While slight alkalinity or acidity does not inhibit, the most favor- 

 able reaction of media is a P w of 7.4 to 7.6. 



H 



Oxygen is necessary for development. Complete anaerobiosis, while 

 not absolutely inhibitory, is extremely unfavorable, unless proper 

 carbohydrates be present. 



Recently, work by Wherry and Erwin, 8 as well as by Gates, 9 has 

 shown that the growth of the meningococcus is definitely stimulated 

 by replacing about ten per cent of the air by carbon dioxide. The 

 plates are placed into a closed jar, into which freshly produced carbon 

 dioxide is allowed to pass, and the jars are then sealed and incubated. 

 This matter has been discussed in a previous section on partial oxygen 

 tensiort in bacterial cultures. We have confirmed this in our labora- 

 tory, and find that the colonies grow larger and growth is more rapid 

 under the partial C0 2 atmosphere. 



While growth may take place at temperatures ranging from 25 

 to 42 C., the optimum is 37.5 C. It is an important aid to the 

 recognition of true meningococci that they never grow at ordinary 

 room temperature. Apart from the remarkable viability displayed 

 upon calcium-carbonate broth, the average length of time during 

 whiclTthe meningococcus will remain alive without transplantation is 

 rather short. Recently isolated cultures grown on agar or serum-agar 

 may die within two or three days. Accustomed to artificial cultivation 

 through a number of generations, however, the cultures become more 

 hardy and transplantation may safely be delayed for a week or even 

 longer. Albrecht and Ghon 10 have kept a culture alive on agar for 

 one hundred and eighty-five days. It is a strange fact that after pro- 

 longed artificial cultivation some strains of meningococcus may grad- 

 ually lose their growth energy and finally be lost because of their 

 refusal to develop in fresh transplants. 



It is our belief that this phenomenon which hitherto we have been 

 at a loss to explain, may have some connection with the so-called 



8 Wherry and Erwin, Jour, of Infec. Dis., 22, 1918, 194. 



8 Gates, Jour. Exper. Med., 29, 1919, 325. 



10 Albrecht und Ghon, Wien. klin. Woch., 1901. 



