A8 MEDIA AND THEIR PREPARATION 
AGAR MEDIA 
Nutrient Agar. 1. Add 3 gms. of beef extract, 5 gms. of peptone 
and 12 gms. of agar dried for one-half hour at 105° C. before weighing 
to 1000 c.c. of distilled water. Boil over a water bath or cook in an 
autoclave until all the constituents are thoroughly dissolved. Make up 
the loss of evaporation. 
2. Cool to about 45° to 50° C. and add 10 gms. of desiccated egg 
albumin per liter. Heat in the autoclave for thirty minutes. Make up 
the loss on evaporation and adjust reaction to 1+. 
3. Filter through cotton or cloth until clear.* Tube and sterilize 
in the autoclave at 120° C. 
Carbohydrate Agar. Any carbohydrate agar which is desired may 
be made by adding 1 per cent of the carbohydrate to plain agar. For 
careful work, carbohydrate media prepared from di- or tri-saccharides 
should not be sterilized in the autoclave as has been shown by Mudge 
(1917) and Hasseltine (1917). 
Litmus Lactose Agar (Bendick, 1913). Bendick has devised the 
following for litmus lactose agar. 
AQOY.. cnn ee teen ee nens 15 gms 
Beef extract......0.. 0. cc cece eee eee eee 5 gms 
Salt... eee eee eee 10 gms 
Peptone.. 2.0... cee eee ee eee 10 gms. 
Lactose 2... 0... cee cee eee eee 20 gms. 
Calcium carbonate............-.0.0 eee eee 4 gms. 
Litmus... 0.00... ee eee ees 100 gms. 
Distilled water... 2.2.0.0... 00.002. e ee ee eee 1000 c.c. 
The agar, beef extract, salt and peptone are dissolved in 1000 c.c. 
of water. This is cleared with egg and filtered. No adjusting of the 
reactions is necessary. This is put into flasks (250 c.c. in a 500-c.c. 
flask). One gram of CaCQOs is added and the whole sterilized. 
Finally to each flask are added 25 c.c. of Kahlbaum’s aqueous litmus 
and 5 gms. of lactose. Tube by pouring direct to the tubes from the 
flasks keeping the contents well mixed. 
Litmus Lactose Agar (Meyer). Meyer (1917) has shown that 
a litmus lactose agar prepared from 3 per cent agar gives plates which 
* The Sharples laboratory centrifuge will give a clear centrifugate in a short time 
with none of the usual trouble and expense connected with filtration through cotton 
or paper. 
