52 MEDIA AND THEIR PREPARATION 
The agar is dissolved in 1000 c.c. H2O. When melted the extract, 
gelatin and salts are added. It is cleared and filtered. Dextrose is 
then added and it is tubed. 
Malachite Green Media (1906). 1. Three gms. Liebig’s meat 
extract. 
2. Acidify this with 7.5 c.c. NHC. 
3. Dissolve 30 gms. agar by boiling. 
4. Neutralize with 7 c.c. NNaOH until neutral to litmus. 
5. Add 5 c.c. NNagCOs3 and heat in an Arnold for several hours. 
6. Add 100 c.c. of 10 per cent sucrose solution. This may be stored 
in 100 ¢.c. quantities. 
7. Before use redissolve and to 100 c.c. add 2 to 2.9 c.c. of 2 per cent 
malachite green (trade mark Hochst 120). This should be made in 
sterile H20 and not boiled. 
8. Medium is smeared in Petri dishes. 
Russell’s Medium (1911). ‘‘ Enough 5 per cent aqueous solution of 
litmus (8 to 5 per cent) is added to plain agar (2 or 8 per cent), which 
usually has a reaction of about 0.8 per cent acid to phenolphthalein, 
to give it a distinct purple violet color, the amount of litmus depending 
on the original color of the agar; dark requiring more than light, and 
the reaction is then adjusted by adding sodium hydrate until the mix- 
ture is neutral to litmus. Next, and last, 1 per cent of lactose and 
one-tenth of 1 per cent of glucose dissolved in a small amount of hot 
water is added and the medium tubed for slants. The sterilization is 
done in the Arnold and because of the danger of breaking down the 
lactose must not be carried too far; if the tubes are packed loosely in 
the sterilizer basket to allow good circulation of the steam, ten minutes 
on the first and fifteen on the second day has been time enough. The 
tubes are then slanted and stored in small quantities in a dark place.” 
Krumwiede has substituted Andrade for the litmus and secured 
good results. 
Endo’s Medium (after Kendall, 1911-12). 
I. Preparation of agar. 
(a) Prepare plain sugar free agar using 15 gms. agar per liter. 
(b) Adjust to a point just alkaline to litmus. 
(c) Place in flasks in 100 c.c. quantities and sterilize. 
