NUTRIENT GELATIN. 99 



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 

 the use of meat-extracts instead of infusion of meat. 

 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 ; 

 affords 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. 



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 completely dissolved, which occurs very rapidly 

 in hot bouillon. The reaction of the gelatin of com- 

 merce is frequently quite acid, so that a much larger 

 amount of alkali is needed for its neutralization thau 

 for other media. It is possible, however, to obtain 

 from the makers an excellent grade of gelatin from 

 which all acid has been carefully washed.^ The gelatin 

 is added in the proportion of 10 to 12 per cent. Its 



'Hesteberg's acid-free, gold-label gelatin has given us entire satis- 

 faction in this respect. It is an imported article. 



