THE PREPARATION OF CULTURE MEDIA 135 



the loss by evaporation with distilled water, and to dissolve the other 

 ingredients in a similar quantity of water, finally mixing the solutions. 

 The mixture is rendered alkaline by the addition of 10 c.c. of normal 

 NaOH, and is cleared, filtered, and filled into test tubes. 



Plates are made with this medium and surface smears made of the 

 suspected material. B. typhosus grows in small, glistening, bluish 

 translucent colonies. Colonies of B. coli are larger, more opaque, and 

 show a brownish tinge. 



Conradi-Drigalski Medium.^ — The following are the directions given 

 by the originators of this medimn for its preparation, (a) Three pounds 

 of meat are infused in two liters of water for twelve hours or more. 

 After straining, boil for one hour and add 20 gms. of Witte's pepton, 20 

 gms. of nutrose, 10 gms. of NaCl; boil one hour and filter. To the filtrate 

 add 60 gms. of agar. Boil for three hours (or one hour in an autoclave) 

 until agar is dissolved. Render weakly alkaline to litmus paper, filter, 

 and boil for half an hour more. 



(b) Litmus solution: Two hundred and sixty c.c. of litmUs solution 

 are boiled for ten minutes. (The litmus solution used by Conradi and 

 Drigalski is the very sensitive aqueous litmus recommended by Kubel 

 and Tiemann, and purchasable under the name.) After boiling, 30 

 grams of chemically pure lactose are added to the litmus solution. 

 The mixture is then boiled for fifteen minutes, and, if a sediment has 

 formed, is carefully decanted. 



(c) Add the hot lactose mixture to the hot fluid agar solution; mix 

 well and, if necessary, again adjust to a weakly alkaUne reaction, litmus 

 paper being used as an indicator. To this mixture add 4 c.c. of a hot, 

 sterile, ten per cent solution of sodium carbonate, in order to render it 

 alkaline, and 20 c.c. of a freshly made solution of crystal violet (c. p. 

 Hochst), 0.1 gram in 100 c.c of sterile distilled water. 



The medimn contains thirteen per cent of litmus solution and one 

 one-thousandth per cent of crystal violet. 



(The plates used by Conradi and Drigalski are large plates 15 to 

 20 cm. in diameter.) Surface smears are made upon the medium after 

 solidification. These are incubated twenty-four hours. Typhoid colonies 

 are small, blue, and transparent. Colon colonies are large, red, and 

 opaque. 



Endo's Medium.^ — 1. Prepare one liter of meat infusion three per 

 cent agar, containing 10 grams of pepton and 5 grams of NaCl. 



1 Conradi-Drigalski, Zeit. f. Hyg., xxxix, 1902. 



2 Endo, Cent, f . Bakt., xxxv, 1904. 



