1 90 Cultivation of Micro-organisms 



standard reaction of media, but with the recommendation that the optimum 

 growth reaction be always recorded with the species." 



BOUILLON 



This is one of the most useful and most simple media. It can be 

 prepared from meat or from meat extract, and is 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." 



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

 chopped lean, boneless beef, 1000 cc. 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 cc. 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 corrected for acidity, 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 according 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 alka- 

 line solution being added drop by drop until a faint blue appears on 

 the red paper; or 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 solu- 

 tion of 5 grams of phenolphthalein 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. After titration the 

 bouillon must again be boiled for a few minutes, in order to precipi- 

 tate the acid albumins, as much water added as has been lost by 

 evaporation, and the fluid filtered through a pharmaceutic filter. 



The filtered fluid is dispensed in previously sterilized tubes with 

 cotton plugs about 10 cc. to each or in flasks, and is then sterilized 

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



