54 



APPLIED BACTERIOLOGY 



through muslin, after which 5 grammes of sodium chloride 

 and 10 grammes of peptone are added ; the mixture is then 

 boiled for five minutes. The lic[uid is now carefully 

 neutralised with a solution of sodium carbonate, and then 

 rendered just faintly alkaline. Should the broth have been 

 made too alkaline, a little dilute lactic acid is added until 

 the proper degree ,of alkalinity is reached. The broth is 

 now poured into a large flask, to which has been added 

 previously 100 to 120 grammes of the finest colourless leaf 

 gelatine. The gelatine is allowed to soak for an hour or so, 



Fig. 12. — Apparatus for Filtering Media. 



when the flask is immersed in a water-bath until the gela- 

 tine is perfectly dissolved. The reaction of the mixture is 

 again carefully tested with litmus, to see if it still remains 

 just alkaline. Owing to the loss of water by evaporation, 

 the volume of the media should be noted, and hot water 

 added until the volume is about 1,100 c.c. The mixture 

 is now cooled, and the white of one egg is carefully and 

 thoroughly mixed in with the gelatine solution, which is 

 then heated in a boiling-water bath for fifteen minutes, or 

 until the whole of the albumin has been precipitated. The 



