80 BACTERIOLOGY. 



to employ the yellow curcuma paper for the detection of 

 alkalinity rather than the red litmus paper. 



Not infrequently, the filtered bouillon, neutralized and 

 sterilized, will be seen to contain a fine, flocculent pre- 

 cipitate. This may be due either to excess of alkalinity 

 or to incomplete precipitation of the albumin. The 

 former may be corrected with dilute acetic or hydro- 

 chloric acid, and the bouillon again boiled, filtered, and 

 sterilized ; or, if due to the latter cause, subsequent boil- 

 ing and filtration usually results in ridding the bouillon 

 of the precipitate. 



Another modification now generally employed is the 

 use of meat extracts instead of the 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 the 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. 



NUTRIENT GELATIN. For the preparation of gela- 

 tin the bouillon is first prepared in exactly the same 

 way as has just been described, except that the neutral- 

 ization takes place after the gelatin has been completely 

 dissolved, which occurs very rapidly in hot bouillon. 

 The reaction of the gelatin as it comes from the manu- 

 factories 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 manufactories an excellent grade of gelatin from 



