CULTURE-MEDIA. 65 



filtered through filter-paper. The filter-paper should be 

 folded and creased as is done by pharmacists; it is in the 

 usual manner placed in a glass funnel, and should be moistened 

 with water before using. After filtration the medium is to be 

 placed in properly plugged tubes or flasks, and is to be sterilized 

 once in the autoclave, or in the steam sterilizer for fifteen min- 

 utes or longer on each of three consecutive days. When pre- 

 cipitates form, they are usually caused by a too alkaline reac- 

 tion. That may be corrected by the addition of a little weak 

 hydrochloric acid, drop by drop, testing frequently with litmus- 

 paper. 



A more accurate way of obtaining the proper reaction is Schultz's method. 

 Take of the bouillon 10 c.c. ; add a few drops of phenolphthalein* (alcoholic 

 solution, J per cent.); with a burette add, drop by drop, a solution of caustic 

 soda, 0.4 per cent., until a faint red color appears, which indicates the beginning 

 of the alkaline reaction. This procedure is followed with three samples. The 

 amount of soda solution required in each case is noted and the average taken. 

 If now, on the average, for each 10 c.c. of bouillon i c.c. of soda solution needs 

 to be added, for 1000 c.c. of bouillon 100 c.c. of the soda solution must be added ; 

 only, instead of adding a weak soda solution, one-tenth as much is taken of a 

 solution ten times as strong. 



Another method of making bouillon and that most usually 

 recommended, is to use, instead of beef-extract, 500 grams 

 (one pound) of finely chopped, lean beef, which is placed in one 

 liter of water and kept on ice for twenty-four hours. It is 

 strained, thoroughly cooked to coagulate the albumen in it, 

 filtered and a liter of fluid obtained, adding water if necessary. 

 The peptone and salt are then added and the medium heated 

 to dissolve them. Some advise the addition of the peptone and 

 salt to the fresh watery extract of the meat before boiling. In 

 preparing media for the purpose of water analysis it is advised 

 to leave out the salt. It is then neutralized, filtered and steril- 

 ized. Although bouillon made with solid beef-extract is con- 



*In neutralizing an acid culture-medium it has been found that when the 

 medium appears to be neutral or slightly alkaline to Htmus. it may still be 

 acid if phenolphthalein be employed as an indicator. Fuller. Journal Ameri- 

 can Public Health Association. 1895. 



