72 MANUAL OF BACTERIOLOGY. 



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

 cipitates form, they are usually caused by a too alkaline 

 reaction. 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 phenol- 

 phthalein 1 (alcoholic solution i per cent.) ; with a burette add, drop by 

 drop, a solution of caustic soda 0.4 per cent, until a faint red color ap- 

 pears, which indicates the beginning of the alkaline reaction. This 

 procedure is followed with three samples. The amount of soda solu- 

 tion 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 1,000 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 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. It is then neutralized, filtered, and sterilized. Al- 

 though bouillon made with solid beef-extract is convenient 

 and serviceable for most purposes, it is advisable to use 

 fresh meat when the bouillon is to be employed for the 

 development of bacterial toxins. Fresh meat should also be 

 used in the preparation of either bouillon, gelatin or agar- 

 agar when new species of bacteria are being studied for pub- 

 lication. 



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

 the medium appears to be neutral or slightly alkaline to litmus, it may 

 still be acid if phenolphthalein be employed as an indicator. Fuller, 

 Journal .-lincrican Public llcaltli Association. 1895. 



