68 MANUAL OF BACTERIOLOGY. 



ence of indol before it is used for diagnostic purposes; since Rivas* finds that 

 in fermenting meat-juice with B. coli by Smith's method for sugar-free broth, 

 indol may be formed. 



Beef-extract 3 grams. 



Pepton . . lo grams. 

 Sodium chloride 5 grams. 



Gelatin (best gold label) . loo grams. 

 Water i liter. 



Dissolve the ingredients in the water, stirring actively to 

 prevent burning at the bottom. It is best to conduct the opera- 

 tions in granite or enamel-ware vessels over a large Bunsen 

 or rose-burner. Neutralize with sodium hydroxide solution 

 (see page 66). Litmus-paper or titration may be used for 

 testing. The reaction at the beginning will usually be found 

 to be quite acid. Allow the mixture to cool until below 6o° 

 C, and add the whites of one or two eggs which have been 

 beaten up with a little water; stir in thoroughly. Heat the 

 mixture to the boiling-point; stir at the bottom to prevent 

 burning and at the same time avoid as far as possible breaking 

 the coagulum of egg-albumen which forms at the surface. 

 Boil for ten minutes. Filter while hot. The filtration may be 

 done through folded filter-paper which has been moistened. 

 It is well to fasten a piece of coarse cheese-cloth over the top of 

 the funnel to catch the large particles of coagulated albumen. 

 Place in suitable tubes or flasks plugged with cotton, and 

 sterilize once in the autoclave, or, preferably, in the steam 

 sterilizer for fifteen minutes on each of three consecutive days. 

 Gelatin is injured by too prolonged boiling and loses its solidi- 

 fying qualities. The remarks on pages 66 to 67 with regard to 

 the use of beef and the titration method for the preparation of 

 bouillon apply equally to gelatin. 



Instead of filter-paper, some prefer to filter through several 

 layers of absorbent cotton placed inside of the moistened glass 

 funnel, the top of which is covered with coarse cheese-cloth. 



* Journal of Infectious Diseases. Vol. IV., No. 4, Nov. 15, 1907, pp. 641-646. 



