NUTRIENT MEDIA 35 



acid or alkali, sufficient alkali may be added to reduce the 

 reaction to the required point. After standardisation, the 

 medium is heated on a water bath for half an hour to bring 

 down the precipitate caused by the change in reaction (mag- 

 nesium ammonium phosphate, Jordan), and then filtered. 



Preparation of Beef Broth. One pound of beefsteak, 

 freed from fat and connective tissue, is cut up and passed 

 through a mincing-machine. The finely-minced meat 

 is digested with 1,000 c.c. of water. It is then boiled, 

 with constant stirring, for thirty minutes in a tinned or 

 enamelled saucepan, which is kept well covered. The 

 broth is strained through muslin, and then made up with 

 distilled water to 1,000 c.c., to replace that evaporated 

 during the boiling. This is the ' acid-beef broth.' To the 

 broth is then added 5 grammes of sodium chloride and 10 

 grammes of peptone. The latter is first rubbed up with a 

 little of the broth in a glass mortar, after which it is added 

 to the bulk. 



The mixture is now boiled for five minutes, and then 

 very carefully neutralized with a solution of sodium car- 

 bonate or hydrate, making the solution very faintly 

 alkaline to litmus-paper. The alkaline solution is added 

 carefully, drop by drop, shaking the flask well between 

 each addition. The solution is again boiled for ten 

 minutes, with constant agitation. The reaction is again 

 tested with litmus -paper, and if still faintly alkaline, the 

 solution is filtered into a flask through a double-pleated 

 filter-paper. Or the broth may be standardized to + 10 

 (vide supra). The filtered product, which should be 

 absolutely clear and bright, is then run into flasks (which 

 are plugged with sterile cotton- wool) and sterilised on three 

 successive days in the steamer for fifteen to twenty minutes 

 on each occasion. Bullock's heart or sheep's heart may 

 be used instead of steak. 



Lemco Broth. Although some workers prefer beef broth, 

 one in which extract of meat is used serves equally for 

 most purposes, and is now generally used. Lemco, 20 

 grammes; peptone, 20 grammes; salt, 10 grammes; 

 distilled water, 1 litre. Boil for thirty minutes, standardise, 

 and filter. This is more easy to prepare, and varies less 

 in composition, than beef broth. 



If, in spite of filtration, the broth remains turbid, the 

 white of an egg is added to the cooled broth (50 C.), 



