32 METHODS OF CULTIVATION OF BACTERIA 



Preparation of Meat Extract. 



The flesh of the ox, calf, or horse is usually employed. 

 Horse-flesh has the advantage of being cheaper and containing 

 less fat than the others ; though generally quite suitable, it has 

 the disadvantage for certain purposes of containing a larger 

 proportion of fermentable sugar. The flesh must be freed from 

 fat, and finely minced. To a pound of mince add 1000 c.c. 

 distilled water, and mix thoroughly in a shallow dish. Set 

 aside in a cool place for twenty-four hours. Skim off any fat 

 present, removing the last traces by stroking the surface of the 

 fluid with pieces of filter paper. Place a clean linen cloth over 

 the mouth of a large filter funnel, and strain the fluid through 

 it into a flask. Pour the minced meat 

 into the cloth, and, gathering up the 

 edges of the latter in the left hand, 

 squeeze out the juice still held back in 

 the contained meat. Finish this expres- 

 sion by putting the cloth and its contents 

 into a meat press (Fig. 6), similar to 

 that used by pharmacists in preparing 

 extracts ; thus squeeze out the last drops. 

 The resulting sanguineous fluid contains 

 the soluble albumins of the meat, the 

 soluble salts, extractives, and colouring 

 matter, chiefly haemoglobin. It is now 

 FIG. 6. Meat press. boiled thoroughly for two hours, by 

 which process the albumins coagulable 



by heat are coagulated. Strain now through a clean cloth, 

 boil for another half-hour, and filter through white Swedish 

 filter paper (best, C. Schleicher . u. Schull, No. 595). Make 

 up to 1000 c.c. with distilled water. The resulting fluid 

 ought to be quite transparent, of a yellowish colour without 

 any red tint. If there is any redness, the fluid must be 

 reboiled and filtered till this colour disappears, otherwise in 

 the later stages it will become opalescent. A large quantity 

 of the extract may be made at a time, and what is not 

 immediately required is put into a large flask, the neck plugged 

 with cotton wool, and the whole sterilised by methods B (2) or 

 (3). This extract contains very little albuminous matter, and 

 consists chiefly of the soluble salts of the muscle, certain 

 extractives, and altered colouring matters, along with any slight 

 traces of soluble proteid not coagulated by heat. It is of acid 

 reaction. We have now to see how, by the addition of proteid 



