BOUILLON MEDIA 33 



1. Bouillon Media. These consist of meat extract with the 

 addition of certain substances to render them suitable for the 

 growth of bacteria. 



1 (a). Peptone Broth or Bouillon. This has the com- 

 position : 



Meat extract l . 1000 c.c. 



Sodium chloride . . . 5 grms. 



Peptone albumin (Witte's) . . 10 



Boil till the ingredients are quite dissolved, and neutralise 

 with a 4 per cent, solution of sodium hydrate. Add the latter 

 drop by drop, shaking thoroughly between each drop and testing 

 the reaction by means of litmus paper. Go on till the reaction 

 is slightly but distinctly alkaline. Neutralisation must be 

 practised with great car.e, as under certain circumstances, 

 depending on the relative proportions of the different phosphates 

 of sodium and potassium, what is known as the amphoteric 

 reaction is obtained, i.e., red litmus is turned blue, and blue red, 

 by the same solution, ^he sodium hydrate must be added till 

 red litmus is turned slightly but distinctly blue, and blue litmus 

 is not at all tinted red. After alkalinisation, allow the fluid to" 

 become cold, filter through Swedish filter paper into flasks, 

 make up to original volume with distilled water, plug the flasks 

 with cotton wool, and sterilise by methods B (2) or (3) (pp. 28, 

 29). This method of neutralisation is to be recommended for 

 all ordinary work. 



In this medium the place of the original albumins of the meat is taken 

 by peptone, a soluble protein not coagulated by heat. Here it may be 

 remarked that the commercial peptone albumin is not pure peptone, but 

 a mixture of albumoses (see footnote, p. 199) with a variable amount of 

 pure peptone. The addition of the sodium chloride is necessitated by 

 the fact that alkalinisation precipitated some of the phosphates and 

 carbonates present. Experience has shown that sodium chloride can 

 quite well be substituted. The reason for the alkalinisation is that it is 

 found that most bacteria grow best on a medium slightly alkaline to 

 litmus. Some, e.g. the cholera vibrio, will not grow at all on even a 

 slightly acid medium. 



Standardisation of Reaction of Media. While the above 

 procedure of dealing with the reaction of a medium is sufficient 

 for ordinary work, it has been thought advisable to have a more 

 exact method for making media to be used in growing organisms, 

 the growth characteristics of which are to be described for 

 systematic purposes. Such a method should also be used in 



3 Some workers, instead of meat extract as made above, use Liebig's 

 extract of beef, 2 grammes to the litre. 



