14 . BACTERIOLOGICAL DIAGNOSIS. 
the fluid is slightly alkaline.* Boil the fluid for half an 
hour to coagulate any albumen which may be present. 
Next filter the broth into a sterile flask, passing it 
through a double thickness of white filter or blotting 
paper, and plug the flask firmly with sterilised cotton- 
wool, 
If the broth is to be used for the manufacture of 
gelatin or agar it is next sterilised in the flask, while 
if it is to be used as it is as a culture medium, it is 
decanted into tubes and then sterilised. 
In decanting media into tubes be very careful not to 
get the plug wet and not to let any of the medium 
get on to the upper part of the tube; otherwise the plug 
will stick to the tube, and there will be some danger of 
bacteria from the air “growing through” the fluid 
contained in the interstices of the plug and contami- 
nating the culture. Ordinary non-absorbent (brown) 
wool is better than the white absorbent wool, as it is 
less easily wetted. 
The broth (and other culture medium after being 
melted) may be poured into the tubes in the following” 
way. A sterilised funnel is united by a short length 
of india-rubber 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, filled 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 
* If during the neutralizing process too mnch alkali is added, then 
it is necessary to re-acidify with dilute hydrochloric acid and re- 
neutralize. The sodium chloride formed makes no practical differ- 
ence in the medium. 
