34 METHODS OF CULTIVATION OF BACTERIA. 



Preparation of Meat Infusion. 



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 looo 

 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 larger 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 expression by putting the cloth and its 

 contents into a meat press (Fig, 7), similar 

 to that used by pharmacists in preparing ex- 

 tracts ; thus squeeze out the last drops. The 

 resulting sanguineous fluid contains the solu- 

 ble albumins of the meat, the soluble salts, 

 .7.— ea press. extracts, extractives, and colouring matter, 

 chiefly haemoglobin. It is now 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, other- 

 wise in the later stages it will become opalescent. A large 

 quantity of the infusion 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 infusion contains very little albuminous matter, and 

 consists chiefly of the soluble salts of the muscle, certain ex- 

 tractives, and altered colouring matters, along with any slight 

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



