58 APPLIED BACTERIOLOGY 



very characteristic growths, cannot be used for temperatures 

 above 20° C, as its melting-point is about 22° C, or a little 

 higher. The nutrient gelatine prepared according to the 

 formula of Koch and Loffler is the one most in use, and is 

 made as follows : One pound of beef-steak is minced, as 

 directed under the preparation of beef-broth, and digested 

 with 1,000 c.c. of water, which is then slowly raised, with 

 stirring, to the boiling-point. The infusion is then strained 

 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 liquid 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, 

 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 

 gelatine is now filtered through a double-pleated filter- 

 paper previously moistened, and kept warm by means of 

 a hot-water funnel ; or, better, the filter can be placed 

 in an ordinary funnel in the steam steriliser until the 

 whole of the gelatine has run through perfectly clear. It 

 will be found best to return the first 100 c.c. of filtrate to 



