PREPARATION OF CULTURE MEDIA. 2I 
and is best purchased ready for use from a good 
laboratory. For clinical purposes it is chiefly used in 
the preparation of the diphtheria bacillus, for which, 
however, it may be replaced by the following medium, 
which is more easy to prepare. 
ASCITIC AGAR :—Requisites :— 
1. Clear ascitic, pleuritic, or hydrocele fluid. 
2. A Io per cent. solution of caustic potash. 
3. Glycerine. 
4. Other materials and apparatus as for agar. (Broth 
is not required, its place being taken by the pathological 
exudate). 
Method.—Measure the fluid and add to it 2 c.c. of the 
potash solution for each 100 c.c. used. Mix thoroughly, 
pour a little into a test-tube, and heat. If the fluid 
does not coagulate proceed with the manufacture of the 
medium in the manner described below. If it coagu- 
lates add a little more potash, mix, and again test. 
The addition of the potash must be repeated until no 
coagulum forms on heating, all the albumen being 
converted into uncoagulable alkali-albumen. 
The remaining steps of the process-are the same.as 
for ordinary agar, except that the neutralisation is 
omitted and 6 c.c. of glycerine per 100 c.c. of the 
medium is added whilst the agar is being dissolved. ~ 
Potato tubes are in occasional use, and are easy to 
prepare. The process is as follows:—Take large and 
sound potatoes and scrub them thoroughly with a nail- 
brush under the tap. Peel them deeply enough to 
remove the eyes completely. Then cut them into 
cylinders a little less than 2 in. in diameter (if you are 
using 2 in. test tubes) and as long as possible; this is 
best done by means of a cork-borer, but. they may. be 
shaped by means of a kmife if this is not at hand. 
