134 . BIOLOGY AND TECHNIQUE 



The solutions are mixed and heated thirty minutes; loss by evaporation is 

 then made up and the solution is filtered through cotton. The reaction is ad- 

 justed to one per cent acidity and the medium tubed 10 c.c. to each tube. 



The typhoid bacillus is characteristic on the Hesse medium only when the 

 dilution poured in the plates is so high that only a few colonies appear. The 

 typhoid colonies are much larger than are the colon colonies and may often.be 

 several centimeters in diameter. 



Conradi-Drigalski Medium. 1 Original directions. 



(a) Three pounds of meat are infused in two liters of water for twelve hours 

 or more. Strain, boil for one hour and add 20 gms. Witte's pepton, 20 gms. of 

 nutrose, 10 gms. of NaCl; boil one hour and filter. 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 lac- 

 tose 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 agar solution; mix well and, 

 if necessary, again adjust to weak alkaline reaction, litmus paper used as an in- 

 dicator. To this mixture add 4 c.c. of a hot, sterile ten per cent solution of 

 sodium carbonate, 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. 



Surface smears are made upon large plates. These are incubated 

 twenty-four hours. Typhoid colonies are small, blue, and transparent. 

 Colon colonies are large, red, and opaque. 



Endo's Medium. 2 1. Prepare one liter of meat infusion three per cent 

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



2. Neutralize and clear by filtration. 



3. Add 10 c.c. of 10% sodium carbonate to render alkaline. 



4. Add 10 grams of chemically pure lactose. 



5. Add 5 c.c. of alcoholic fuchsin solution, filtered before using. (Endo in 

 his original contribution does not mention the strength of this fuchsin solu- 

 tion, which, however, should be saturated. This colors the medium red. 



6. Add 25 c.c. of a 10% sodium sulphite solution. This again decolorizes 

 the medium, the color not entirely disappearing, however, until the agar is 

 cooled. 



7. Put into test tubes, 15 c.c. each, and sterilize. 



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



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



