88 ABSTRACTS 



4. No indicator, used for the titration of media is accurate in all 

 cases (even phenolphthalein which is very sensitive to acids will not 

 indicate phosphoric acid accurately when it is in mixtures). 



5. Enough media should be used for titration so that inaccuracies 

 in measuring are minimized and errors in the actual titration will not 

 be magnified in subsequent calculations. 



6. The acid equivalent of media varies with the temperature of the 

 media and the amount of variation is dependent upon the compounds 

 present in the media. 



7. Media should be added to carbon dioxide free distilled water and 

 titrated at the temperature at which they are to be held when organisms 

 are growing. 



8. Distilled or double distilled water does not mean carbon dioxide 

 free water. The carbon dioxide content of distilled water will not be 

 a constant from day to day at a given laboratory. 



9. Carbon dioxide in distilled water makes it possible to have a 

 medium titrate, with phenolphthalein, 1.0 per cent acid^ when it is alka- 

 line or neutral. 



10. The acidity of media that has been properly made does not 

 increase appreciably when the length of time of sterilization is increased 

 or when repeated sterilizations are made in the autoclave. 



A Culture Medium for Maintaining Stock Cultures of the Meningococcus. 



C. G. A. Rocs. 



This medium has been in use for about two years and experience has 

 demonstrated its superiority over the other media mentioned in the 

 literature for the maintenance of stock cultures of the meningococcus. 

 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 2 hours 100 gm. 



b. Water containing 4 per cent doubled distilled glycerine free 



from acid 200 c.c. 



c. Mix and autoclave for 40 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 c.c. 



NaCl Sol. 0.65 per cent 150 c.c. 



Agar 5 gm. 



6. Heat in Arnold sterilizer until agar is melted, requiring from 30 min. 

 to 1 hour. 



3. Tube and sterilize without filtering in autoclave for about 40 minutes. 



4. When wanted for use, melt the agar, cool back to about 45°C. and add 



the desired amount of defibrinated horse blood. 



' Requires 10 cc. of normal alkali per liter to make it neutral. 



