CULTIVATION OF BACTERIA. 107 



enough water added to bring the total amount up to 1000 

 c.cm. This liquid is called the meat-infusion. To it 

 10 grams of Whitte's dried beef-peptone and 5 grams of 

 sodium chlorid are added, and the whole boiled until the 

 albumins coagulate. The reaction is then carefully tested, 

 in order that whatever sarcolactic acid may have been 

 present in the meat may be neutralized by the addition 

 of a few drops of a saturated aqueous solution of sodium 

 carbonate. The solution is added drop by drop, and the 

 reaction frequently tested with litmus-paper. When a 

 neutral reaction, or, better, a faint alkaline reaction, is 

 attained, the mixture is well stirred, boiled again for 

 about half an hour, to precipitate the alkaline albumins 

 formed, and filtered. The bouillon thus prepared is a 

 clear fluid of a straw color, much resembling normal 

 urine in appearance. It is dispensed in tubes about 10 

 c.cm. to each and is then sterilized by steam three suc- 

 cessive days for fifteen to twenty minutes each, according 

 to the directions already given for fractional sterilization. 

 (See p. 94.) 



For the preparation of bouillon, as well as gelatin, 

 agar-agar, and glycerin agar still to be described, beef- 

 extract (Liebig's) may be employed, but for the most 

 delicate work this is rather undesirable, because of its 

 unstable composition and because of the precipitation of 

 meat-salts, which can scarcely be filtered out of the agar- 

 agar, owing to the fact that they only crystallize when 

 the solution cools. When it is desirable to prepare the 

 bouillon from beef-extract, the method is very simple. 

 To 1000 c.cm. of clean water 10 grams of Whitte's dried 

 beef-peptone, 5 grams of sodium chlorid, and about 2 

 grams of beef-extract are added. The solution is boiled 

 until the constituents are dissolved, neutralized, if neces- 

 sary, and filtered when cold. If it is filtered while hot, 

 there is always a subsequent precipitation of meat-salts, 

 which clouds it. 



Bouillon and other liquid culture-media are best dis- 

 pensed and kept in small receptacles test-tubes or flasks 



