Differentiation of Typhoid and Colon Bacilli 659 



evaporation. Pour the two solutions together and heat for thirty minutes 

 and add distilled water to replace loss by evaporation. Filter through 

 cotton until clear. Adjust reaction to i per cent, acidity. Tube 10 

 c.c. to a tube. Sterilize in the autoclave. 



The medium is used for plating. The material containing 

 the micro-organisms must be so dilute that only a few colonies 

 will develop upon the plates. The typhoid colonies greatly 

 outgrow the colon colonies and may attain to a diameter of 

 several centimeters. They show a small opaque center and 

 an opalescent body and appear circular. 



Capaldi* recommends the following medium for plating 

 typhoid and colon colonies: 



Witte's peptone 20 grams 



Gelatin 10 



Agar-agar 20 



Dextrose or mannite 10 



Sodium chlorid 5 



Potassium chlorid 5 



Distilled water 1000 



Dissolve the agar in 500 c.c. of water, the other ingredients in the 

 other 500 c.c. of water. Pour together, add 10 c.c. of NaOH, filter, and 

 tube. 



Upon this medium the typhoid colonies are small, glisten- 

 ing, bluish, and translucent. Colon colonies are larger, 

 opaque, and brownish. 



Endo f recommends the employment of the following me- 

 dium upon which colonies of the typhoid bacillus grow large 

 and remain colorless, while those of the colon bacillus remain 

 small and red: 



1000 c.c. of meat infusion. 

 30 grams of agar-agar. 

 10 grams of peptone (Witte's). 

 5 grams of sodium chlorid. 



Neutralize and clear by filtration, then add 10 c.c. of a 10 per cent, 

 solution of NaOH to alkalinize, 10 grams of chemically pure lactose and 

 5 c.c. of a filtered, saturated, alcoholic solution of fuchsin. Next add 

 25 c.c. of a 10 per cent, sodium sulphate solution, by which the intense 

 red given by the fuchsin is entirely bleached by the time the agar-agar 

 is cold. After adding the necessary reagents and while still warm and 

 perhaps red, tube the medium. The tubes should be kept in the dark. 



* "Zeitschrift fur Hygiene," 1896, xxm, 475. 

 t "Centralbl. f. Bakt.," etc., 1904, xxxv. 



