THE PREPARATION OF CULTURE MEDIA 161 



medium. Add about 1 c.c. of decolorized fuchsin solution, made up as above 

 by mixing roughly prepared 10 per cent sodium sulphite with saturated 

 alcoholic fuchsin. (The proportions of fuchsin and sulphite are sometimes 

 difficult to adjust, possibly by reason of impurities in the sulphite due to 

 formation of sulphate. The instructions given by most workers at present 

 are to use 10 c.c. of a 10 per cent aqueous solution of sodium sulphite, 

 and to add to this 1 c.c. of a 10 per cent solution of fuchsin in 96 per cent 

 alcohol.) When these flasks containing the various ingredients are hot they 

 are red or pink, but when plates are poured and allowed to harden, the 

 medium should be either colorless or very faintly pinkish. It is best to pour 

 a number of plates rather thickly and then allow them to dry with the 

 covers off. Inoculations from the feces suspension are then made by surface 

 smear, with a bent glass rod. Colon colonies are pinkish and red; typhoid 

 colonies, smaller and grayish. 



In concluding the description of some of the most important typhoid 

 isolation media, we would like to add that a great deal seems to depend 

 upon the habit-acquired skill which the individual worker attains. None of 

 these stool isolation media are ordinarily successful at once in the hands 

 of anyone, and a certain amount of practice must be attained before one can 

 judge of the usefulness or uselessness of a medium. 



Brilliant Green Agar for Typhoid Isolation. Krumwiede has 'recently 

 devised a brilliant green agar with which he has had excellent results. 26 



The basis is an extract agar like that used for Endo's medium : 



Beef Extract 0.3% 



Salt 0.5% 



Peptone 1.0% 



Agar 1.5% 



(Domestic peptones are satisfactory.) 



Dissolve in autoclave; clear and filter. A clear agar is essential. The 

 final reaction of the medium is to be neutral to 27 Andrade's indicator, which 

 in terms of phenolphthalein is 0.6-0.7% acid (normal HC1) or P^ 7.2. It is 

 more convenient to have the reaction set slightly alkaline to litmus at the time 

 of preparation and to acidify each bottle as used. The agar is bottled in 

 100 c.c. amounts and autoclaved. When needed, the bottles are melted and 

 the volume of each corrected (if necessary) to an approximate 100 c.c.. Add 

 to each bottle: 



28 We are indebted to Dr. Krutnwicde for a preliminary account of this method. 



21 Andrade's Indicator: 0.5 per cent aqueous acid fuchsin 100 c.c. 



Normal NaOH 16 c.c. 



The dye is slowly (2 hours) alkalinized to the color-base; the red tint is restored 

 by acids. 



