234 BACTERIOLOGY. 



Bouillon. 



The meat extract is prepared according* to the directions 

 given under the preparation of gelatin (p. 153). To 1 

 liter of the meat extract, 10 g. of dry pepton (Witte's) and 

 5 g. of common salt are added. The liquid is then warmed 

 at 55-60, with constant stirring, till the pepton dissolves. 

 It is then rendered alkaline according to the directions 

 given on p. 154. The portions of 10 c.c. of the solution in 

 test-tubes should receive 0.4, 0.6, 0.8 and 1.0 c.c. of the -fs 

 NaOH, respectively. The neutral point is usually reached 

 by the addition of about 0.5 c.c. & NaOH per 10 c.c. The 

 remaining liquid is measured and amount of N NaOH nec- 

 essary to neutralize the entire amount is then calculated. 

 This calculated amount, plus 10 c.c. of N NaOH per liter, in 

 order to impart a slight alkalinity, is then added. The 

 liquid is then placed in the enamelled jar (Fig. 23, p. 153), 

 and immersed in a boiling water-bath, or boiled directly 

 over the flame for ^ an hour. Inasmuch as there will be 

 a considerable loss of water by evaporation, it is advisable 

 to mark the level of the liquid, before boiling. At the 

 close of the operation sufficient distilled water should be 

 added to bring the liquid back to the original volume. A 

 better procedure is to weigh the liquid, before and after 

 boiling, and for the number of grams lost in weight to add 

 a corresponding number of c.c. of distilled water. 



The liquid is then filtered through a wet filter. The 

 filtrate is usually perfectly clear and transparent, but it. 

 not infrequently happens, when it is placed in tubes and 

 sterilized, that a fine amorphous precipitate will form. 

 Usually this is unimportant, but, at times, it is desirable to 

 have a bouillon which will remain perfectly clear, free from 

 the slightest deposit. To obtain this result, the filtered 

 bouillon is returned to the clean, enamelled jar and sub- 

 jected to more heat. It can be placed in the autoclave and 



