168 APPENDIX 



egg mixed with a little distilled water is added. The contents 

 are coagulated by heating in current steam in the usual way, 

 filtered, and the filtrate made up to I litre. The mixture is 

 made neutral, litmus paper being used as the indicator. Then 

 19 c.c. of normal sodium carbonate solution and 10 grammes 

 of chemically pure lactose are added. The flask is replaced for 

 thirty minutes in the steam sterilizer. Almost invariably there 

 is a considerable precipitate, and the mixture has to be again 

 filtered. 



Seven c.c. of the fuchsin solution (see below) are added, 

 followed by 25 c.c. of a quite freshly prepared 10 per cent, sodium 

 sulphite solution. The mixture becomes much less red, but 

 is not immediately decolorized. It is then tubed, conveniently 

 into small flasks, each containing 50 to 60 c.c. of media, and 

 sterilized in current steam for two days, thirty minutes each day. 



Thefuchsm solution is made as follows : 



Three grammes of powdered crystalline fuchsin are placed 

 in a dry flask, and 60 c.c. of absolute alcohol are added. The 

 contents are thoroughly well mixed, and the flask, tightly 

 stoppered, allowed to stand for exactly twenty-four hours at 

 20 to 22 C. The alcoholic extract is then decanted and 

 preserved in a clean glass-stoppered bottle. Made in this way a 

 uniform fuchsin extract is obtained which keeps well, and the 

 same quantity of fuchsin is added each time a fresh batch of 

 medium is prepared, a matter of much importance. 



The medium must be stored in the dark, since light gradually 

 turns it red. When solidified it is almost free from colour. 



B. coli colonies are bright red, round, and have prominent 

 margins ; B. typhosus colonies are round, colourless, very trans- 

 parent, and have thin margins. 



Drigalski-Conradi Agar. To 3 pounds of finely-cut-up beef 

 or horseflesh add 2 litres of water. Allow the mixture to stand 

 until next day. Boil the expressed meat-juice for one hour and 

 filter ; add 20 grammes peptone sicca (Witte), 20 grammes 

 nutrose, 10 grammes sodium chloride ; boil the whole again for 

 one hour and then filter. Add 70 grammes bar agar, boil for 

 three hours (or one hour in the autoclave), render slightly 



