60 MEDIA AND THEIR PREPARATION 
Porato AND STarcuH MEpIA 
Potato Gelatin (Goadby). Add 100 gms. of gelatin to 1 liter of 
glycerol potato broth. Boil, adjust the reaction, filter, and sterilize. 
Glycerol Potato Broth. Wash, peel and grind 1000 gms.:of potato. 
Soak this in a liter of water for twenty-four hours. After filtering 
add 3 to 5 per cent of glycerol and tube for sterilization. 
Potato Agar (McBeth, 1913). Pare, steam, and mash a quantity of 
potatoes. To 100 gms. of mashed potato add 800 c.c. of tap water and 
steam for one-half hour, filter through cotton. 
AQOl.. cee tee cence nees 15 gms. 
Nutrient solution (same as for cellulose agar). 500 c.e. 
Starch Agar. Make 1 liter of ordinary peptone agar. Add to this 
a 2 per cent paste of potato starch. This should be added at as low 
a temperature as possible to the neutral agar. 
To use, pour plates with the sterile tubed starch agar and streak 
with the culture. After incubation for 5 days, pour over weak solution 
of Lugol’s iodine. 
Starch Agar (Vedder, 1915). Prepare a liter of beef infusion in 
the usual way. Meat extract does not give as good results. To 
this add 1.5 per cent of agar. No peptone or salt should be added. 
Cook and clarify the medium and add 10 gms. of cornstarch to each 
liter. The starch is best rubbed up in a mortar in a little agar. One 
per cent of starch gives the best results. Tube and sterilize in the usual 
manner. This medium is especially valuable in the growth of gonococci. 
Elsner’s Potato Medium. 1. Peel and grate 500 grams of potato. 
2. Grind up and soak in distilled water for twelve hours. 
3. Strain and allow to stand. Filter to clear. 
4. Make up to 1 liter and dissolve 15 per cent of gelatin. 
5. Adjust reaction to acid and sterilize. 
Potato Infusion. Wash and grind up a few potatoes. To each 
30 gms. of potato, add a liter of distilled water and allow to stand 
in the icebox over night. In the morning, filter and boil the filtrate. 
Filter again if necessary and tube for sterilization. If the infusion is too 
acid adjust the reaction as usual. 
Carrot Infusion. This medium may be prepared as above for 
potato infusion. 
Potato Mash. Clean and cut a large potato into slices. Boil until 
soft and grate or press through a ricer. Distribute this in layers in 
