82 MICROBIOLOGY 



ployed in cultivating bacteria. It is practically a beef tea 

 containing peptone and salt. There are several methods rec- 

 ommended for making it. It may be made directly from sim- 

 ple meat infusion or from meat extract. When meat extract 

 is used, the bouillon does not seem to be a favorable culture 

 fluid for certain bacteria. As the extracts are not uniiorm 

 in the quantities of the various salts, it is impossible to 

 make bouillons of a uniform composition froin them. Bouil- 

 lon is used as the nutritive base in preparing agar and gela- 

 tin. 



Preparation of bouillon. In preparing bouillon the fol- 

 lowing method has been found to be very satisfactory. Take 

 500 grams of lean beef, remove all fat, and grind it in a 

 sausage machine or have it minced at the butcher shop. Place 

 the minced meat in an agate-iron dish, add 1000 cc. (2 parts 

 water to one of meat) of clear boiled water, cooled to 65 C., 

 and stir thoroughly with a glass rod. Then macerate it, with 

 frequent stirring, in a water bath at a tem- 

 perature of 60 C. for one hour after the 

 temperature of the meat and water reaches 

 that of the water outside or, to save time, at 

 a temperature of 65 C. for 30 minutes. Re- 

 move the meat by straining the liquid 

 through a piece of cheese cloth. For this a 



stout iron meat press is desirable. Boil the 

 Fig. 83. Wire 



basket lor hold- str amed meat infusion for 20 minutes. Cool 

 ing tubes. to harden the fat, and filter through filter 



paper. The filtrate should equal in quantity 

 the amount of water used ; if it does not, add enough distilled 

 or clear boiled water to make up that amount. To this meat 

 infusion add 1% peptone (white peptone free from sugar) 

 and 1/2% sodium chloride. Add enough of a normal solution 

 of sodium hydrate to give the liquid a faintly alkaline reac- 

 tion when litmus is added as an indicator. It is simpler to 

 titrate. The infusion is then boiled in a water bath for three 

 quarters of an hour and filtered hot. The filtrate should be 

 perfectly clear. The color will vary according to the amount 



