I 



GELATIN AND POTATO MEDIA. 153 



tion of a beef-tea into a transparent, solid, and easily lique- 

 fiable medium. 



Preparation of Nutrient Gelatin. 



Place 500 g. of chopped, lean beef in an enamelled jar, 

 such as is shown in Fig. 23. This has a capacity of 

 liters. Now add 1000 c.c. of tap- water and 

 stir thoroughly. Immerse the jar in a water- 

 bath, and warm gently, till the temperature of 

 the meat suspension reaches 55-60. l Main- 

 tain this temperature .for f-1 hour, stirring 

 frequently. The soluble constituents are thus 

 brought into solution. Special care should be 

 taken not to allow the temperature to rise 

 above 60, inasmuch as the albuminous sub- 

 stances would then coagulate. By keeping m fki g 2 m e dm. r for 

 these in solution at this stage, they will sub- 

 sequently assist in clarifying the final product, and hence, 

 the addition of a white of an egg will be unnecessary. 



When the digestion is completed, strain the liquid 

 through muslin and thoroughly squeeze the residue. The 

 filtrate is dark red in appearance and should measure 1000 

 c.c. [If this is not the case, add water to make up this 

 volume. To 1000 c.c. of the filtrate returned to the clean 

 jar, now add 



100 g. of gelatin, 



10 g. of dry pepton (Witte's), 



5 g. of common salt, 



and warm at 60, in the water-bath, with constant stirring, 

 till the gelatin has completely dissolved. The next step is 

 to render the liquid slightly, but distinctly alkaline. 



1 A thermo-r emulator may be used to maintain a constant temper- 

 ature in the water-bath (see Chapter IX, also Fig-. 75). 



