ANIMAL INFUSIONS. 107 



of water being added to a pound of the meat. From time to time 

 during this process the whole should be well stirred. It is 

 then filtered through a piece of fine linen cloth, and the pulpy mass 

 is subjected to pressure in the screw press (see Fig. 31), to extract as 

 much fluid as possible from it. The broth thus obtained is usually 

 distinctly acid (see § 43, p. 73), and must be neutralised by the 

 addition of a saturated solution of carbonate of soda, drop by drop, 

 until the broth becomes quite neutral in its reaction. 



It is now received into a glass flask (one litre), and is placed in the 

 steam steriliser at 100° C, and steamed (not boiled) for thirty 

 minutes. A fine precipitate is found to occupy the lower layers of 

 the flask after this process. This is got rid of by filtering the broth 

 through a filter which has immediately previously been washed 

 thoroughly with boiled distilled water, and the clear filtrate is re- 

 ceived into stock flasks (quarter litre), which, with their plugs, have 

 been previously sterilised by superheating (see £ 43, p. 75). The 

 stock - flasks thus charged are steamed for thirty minutes in the 

 steam steriliser at ioo ; C. on each of two consecutive days, standing 

 in a cool place in the intervals of steaming. The stock-flasks are 

 incubated for four days at 32' C, and if no reaction occur, they may 

 be kept as a reservoir of sterile material for future use in cultivation. 



To carry on cultivations with the sterile broth thus prepared, it is 

 convenient to have it divided into small quantities. For this purpose 

 a number of one ounce Bohemian flasks are prepared, supplied with 

 cotton wool plugs, and sterilised by superheating in the hot air 

 chamber (Fig. 33); and 10 c.c. of the sterile broth is transferred to 

 each flask by the use of a superheated glass pipette, as described 

 under "nutrient jelly" (§ 44, p. 78). This should either be carried 

 out under the carbolic spray (footnote, p. 78), or, when charged, 

 the small flasks should be steamed at ioo J C. on two successive 

 days, for fifteen minutes each day. 



Inoculations are carried out by means of a platinum wire as already 

 described, with the exception that here the flasks cannot be inverted 

 to avoid atmospheric contamination, and in this case it is best to 

 inoculate with seed material, either under the spray, or under the pro- 

 tection of a canopy of cotton cloth soaked in a one per cent, solution 

 of perrhloride of mercury. Any of these infusions may be rendered 



