56 MEDIA AND THEIR PREPARATION 
Litmus Gelatin. This may be prepared from lactose gelatin the 
reaction of which must be neutral. Deposit 1 c.c. of sterile litmus 
solution in the sterile Petri dish with the sample and pour in the melted 
gelatin. Shake the dish until the litmus is evenly distributed through- 
out. Incubate at 20° C. This medium is of much value in studying 
the bacteria in milk. 
Hiss Medium (1902). 
AGAP.. 6 eee eee eee ene 15 gms. 
Gelatin. 2.00... ccc eee nae 15 gms. 
Liebig’s meat extract..............0 000008 5 gms. 
Sodium chloride.. ......0. cee ee eee ee eee 5 gms. 
Dextrose... cee cee 10 gms. 
Distilled water... 0.0.0... cece ee eee 1 liter 
Adjust the reaction to 1+. 
Raisin Gelatin (Besson). Make a decoction of raisins by grinding 
and stewing 50 to 100 gms. of raisins in 1000 gms. of H2O for one hour. 
Filter and add 100 gms. of gelatin and a pinch of sodium phosphate. 
Boil for two or three minutes. Neutralize and finish as usual. 
Wort Gelatin. 1. Measure out 900 c.c. of beer wort in sterile flask. 
2. Weigh out 100 gms. gelatin (10 per cent) and add it to the wort 
in the flask. 
3. Bubble live steam through for ten minutes to dissolve the gelatin. 
4. Cool to 60° C., clarify with egg. 
5. Filter and tube. 
Gelatin Agar (Besson). By mixing agar and gelatin a medium is 
obtained with a melting-point between that of either plain agar or plain 
gelatin. 
Peptone broth... 0.0.0... 00... c cece eee ees 1000 gms. 
Gelatin. 20.00.00 coc cece eens 80 gms. 
AQAl. ccc eee eee beeen eens 5 gms 
Or 
Gelatin. ©. 00... cee ce eee 50 gms. 
FN: , 8 gms. 
Dissolve the gelatin in the broth, neutralize and then add the agar. 
Sterilization must not be accomplished above 115° C. (See North’s 
Agar Gelatin Medium.) 
