32 METHODS OF CULTIVATION OF BACTEKIA 



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 traees 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 boiled 

 Fig. 6.— Meat press. thoroughly for two hours, by which pro- 

 cess 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. 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 and other matter, it may be transformed into 

 proper culture media. 



