PREPARATION OF CULTURE MEDIA. 19g 
Acar is the name given to the dried strips of a 
Japanese sea-weed. It forms a jelly which differs from 
that containing gelatin in that it melts at a higher 
temperature; nutrient agar as used in the laboratory 
melts just below the boiling point of water and sets at 
about 40°C. This is an advantage in the cultivation 
of most pathogenic bacteria, for these grow (as a rule) 
best at or near the temperature of the body, the 
temperature to which they are exposed under natural 
circumstances; and at this temperature gelatin would 
melt. Agar is somewhat difficult to prepare unless the 
practitioner has an autoclave, and may be bought with 
advantage. But the following method is not very 
difficult, and, as agar is perhaps the most generally 
useful of all media, should be learnt. 
Reqwisites :—1. Broth. 
2. Agar-agar. This should be cut up into very small 
pieces with a pair of scissors, or may be bought in 
powder. 
3. Solution of acetic acid. (Glacial acetic acid 2-4 
c.c., water 500 C.C.). 
4. A large beaker. 
5. Other apparatus and materials as for gelatin. 
Method.—Weigh out 2 grammes of agar for each 109 
c.c. of broth to be used, and soak it in the dilute acetic 
acid for a quarter of an hour. Now strain off the acid 
and wash the agar in water until a small piece does not 
redden blue litmus paper when pressed upon it. Place 
the broth in a glass beaker and add the agar. Now 
place the beaker upon a piece of wire gauze upon a 
‘tripod stand, and apply a small Bunsen flame or spirit 
lamp; this must be placed so that the flame impinges 
on a point not far from the side of the beaker. As the 
fluid is heated it will rise and a continual circulation 
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