176 Culture Media and Bacteria Cultivation 



the basis of most of the culture media. The addition of 10 

 per cent, of gelatin makes it "gelatin" ; that of i per cent, of 

 agar-agar makes it "agar-agar." The preparation of these 

 media, however, requires special directions, which will be 

 given below. 



I. To Prepare Bouillon from Fresh Meat. To 500 grams 

 of finely chopped lean, boneless beef, 1000 c.c. of clean water 

 are added and allowed to stand for about twelve hours on 

 ice. At the end of this time the liquor is decanted, that 

 remaining on the meat expressed through a cloth, and then, 

 as the entire quantity is seldom regained, enough water 

 added to bring the total amount up to 1000 c.c. This 

 liquid is called the meat-infusion. To it 10 grams of Witte's 

 or Fairchild's dried beef-peptone and 5 grams of sodium 

 chlorid are added, and the whole boiled until the albumins 

 of the meat -infusion coagulate, titrated or otherwise cor- 

 rected for acidity, then boiled again for a short time, and then 

 filtered through a fine filter-paper. It should be slightly 

 yellow and perfectly clear and limpid. Smith,* referring to 

 bouillon intended for the culture of diphtheria bacilli for 

 toxin, says that when the peptones are added before boiling 

 most of them are lost, and therefore recommends that the 

 meat-infusion be boiled and filtered and the solid ingredients 

 added and dissolved subsequently. The reaction, which is 

 strongly acid, is then carefully corrected by titration accord- 

 ing to the directions already given. 



For rough work in students' classes litmus paper may 

 be used as an indicator for determining and correcting the 

 acidity resulting from the sarcolactic and other acids in the 

 meat-infusion, the alkaline solution being added drop by 

 drop until a faint blue appears on the red paper; or the 

 method of using phenolphthalein can be employed, the 

 addition of the alkaline solution being continued until a drop 

 of the bouillon produces a red spot upon phenolphthalein 

 paper, made, as suggested by Timpe, by saturating bibulous 

 paper cut into strips with a solution of 5 grams of phenol- 

 phthalein to i liter of 50 per cent, alcohol. Acids do not 

 change the appearance of the paper, but small traces of alkali 

 turn it red. 



If the bouillon is to be employed for exact work, these 

 crude methods should not be adopted, but chemical titration 

 according to the method already given should be performed. 

 * "Trans. Assoc. Amer. Phys.," 1896. 



