102 BACTERIOLOGY. 



and sterilized, will be seen to contain a fine, flocculent 

 precipitate. This may be due either to excess of alka- 

 linity or to incomplete precipitation of the albumin. 

 The former may be corrected with dilute acetic or 

 hydrochloric acid, and the bouillon again boiled, fil- 

 tered, and sterilized ; or, if due to the latter cause, sub- 

 sequent boiling and filtration usually result in ridding 

 the bouillon of the precipitate. 



Another modification now generally employed is in 

 the substitution of meat-extracts for chopped meat in 

 making the bouillon. Almost any of the meat-extracts 

 of commerce answer the purpose, though we usually 

 employ Liebig's. It is used in the strength of from 

 two to four grammes to the litre of water. Peptone and 

 sodium chloride are added as in the bouillon made from 

 meat-infusion. The advantages of meat-extract are : 

 it takes less time; aifords a solution of more uniform 

 composition if used in fixed proportions ; and in general 

 use gives results that are equally as satisfactory as those 

 obtained from the employment of infusion of meat. 

 The disadvantage is the possible presence of antiseptics 

 or preservatives. 



NUTRIENT GELATIN. For the preparation of gelatin 

 the bouillon is first made in the way given, except that 

 its reaction is corrected after the gelatin has been com- 

 pletely dissolved, which occurs very rapidly in hot 

 bouillon. The reaction of the gelatin of commerce is 

 frequently quite acid, so that a much larger amount of 

 alkali is needed for its neutralization than for other 

 media. It is possible, however, to obtain from the 

 makers an excellent grade of gelatin from which practi- 



