PREPARATION OF CULTURE MEDIA Q 



funnel is united by a short length of indiarubber tubing to a 

 piece of glass tubing drawn out to a point; the rubber tube is 

 clipped by a spring clip or a pair of pressure forceps. The 

 funnel is now mounted on a retort-stand, rilled with the 

 medium, and covered over with a piece of glass. The cotton- 

 wool plug is removed from a. test-tube, and the latter placed 

 so that the glass tube attached to the funnel reaches nearly to 

 the bottom. The clip is released, and the requisite quantity 

 of broth (enough to fill the tube to the depth of i J or 2 inches) 

 is allowed to run in; the clip is then reapplied and the tube 

 removed and plugged. This process is repeated until enough 

 tubes have been filled. 



The tubes and the broth which remains over (after having 

 been poured back into the flask and the latter plugged with 

 cotton-wool) are now sterilized. The vessels are placed in 

 the steam sterilizer and exposed to steam for half an hour on 

 three successive days; this process is called intermittent steri- 

 lization, and its rationale is very simple. The first steaming 

 destroys all developed bacteria, and would sterilize the fluid 

 entirely if no spores were present. In the interval between 

 the first and second sterilization most of the spores which may 

 be present will develop into mature bacteria, and these will be 

 killed by the second steaming. The third sterilization is to 

 kill off any bacteria which may not have developed from spores 

 in the first interval. A very similar process is adopted by the 

 gardener in freeing: soil from weeds; the application of 

 chemical weed-destroyers or a thorough hoeing will destroy 

 developed plants, but will not injure seeds which may be con- 

 tained in the soil, and these processes are repeated, intervals 

 being allowed to permit the development of the plants, until 

 they reach the stage in which they are vulnerable. 



To recapitulate: Mix the ingredients, and heat until they 

 are dissolved, render sligiitly alkaline, boil half an hour, filter. 

 Then place in sterilized flask or into test-tubes, and sterilize in 

 the steam sterilizer for half an hour on three successive days. 



Witte's peptone has been the standard for use in making broth, 

 etc., in the past. Chapoteau's peptone is certainly as good, perhaps 

 better, and is obtainable at the present time. But a better medium, 

 though one a little more difficult to make, is that devised by Captain 

 Douglas, in which peptone is formed in the broth itself by tryptic 

 digestion. It can be very strongly recommended, as it gives much 



