73 



sulphuric acid and one drop of a o.oi per cent, sodium nitrite solution to a 

 four-day peptone-broth culture. If a pink color appears at the end of one- 

 half hour it indicates the presence of indol. 



G. Beef Broth. This medium is now not as extensively used as for- 

 merly. It is more difficult to prepare, and shows no advantages over the 

 bouillon already described. 



Ground or Chopped Lean Beef, 



Peptone, 



Salt, 



Distilled Water, 



500 gm. 



10 gm. 



5 gm. 



IOOO CC. 





FIG. 22. This is a copper double-walled incubator covered with non-conducting 

 material and provided with a water gauge, tubulations for thermometer and thermostat, 

 a ventilating strip, enclosed base and inner glass door. The incubating chamber is 

 24 cm. high, 30 cm. wide and 24 cm. deep. 



Add the water to the minced meat, shake frequently, and keep on ice 

 for twenty-four hours, then strain forcibly through cloth, or press out in a 

 hand press. Add the salt to the liquid, boil, make up to 1000 cc., and 

 add the peptone. Titrate to reaction of + i.o per cent., filter, and 

 sterilize. It will be apparent that the cold water meat infusion con- 

 tains merely the meat salts, meat sugar, and acids, and a certain proportion 

 of the albumens. The albumens are coagulated and removed in the 

 filtering process, so that nothing remains of the meat but the salts, 

 acids, and the trace of muscle sugar. Nearly the whole of the meat 

 proper is wasted. It is apparent, therefore, that the meat extract 

 bouillon answers all the purposes of the beef broth. 



