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 A 

 NaOH, respectively. The neutral point is usually reached 

 by the addition of about 0.5 c.c. ft 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 (Pig. 23, p. 153), 

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

 over the flame for i 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 voluitti^. A 

 better prpcedure is to weigh the liquid, before and after 

 boiling, and for thfe 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 



