POTATO AND STARCH MEDIA 61 
Petri dishes and sterilize at 120° C. for twenty minutes. The slices 
may be placed in the Petri dishes without mashing if desired. 
Starch Jelly (Smith, 1898). To 10 cc. of Uschinsky’s solution 
add 1 gm. of clean aseptic starch. Rub this up in the slanted fluid. 
Plug the tubes tightly and place in an inspissator or Arnold in the 
slanted condition. Heat for two hours on five successive days at 
85 to 93° C. If water is lost, this must be made up by the addition of 
distilled water. 
Potato Agar (Thomas, 1906). The potatoes are carefully washed, 
pared, sliced, then slowly heated for two hours in approximately two 
volumes of water. At the close of the heating the water is allowed 
to boil. The whole is then filtered through cloth, water being added 
to make up the loss of any evaporation. After filtering, 1 per cent 
shred agar is added to this fil rate. It may then be heated in an auto- 
clave for thirty minutes at 15 lbs. after which it may be tubed or fil- 
tered, if desired, before tubing. 
Cellulose Agar (McBeth, 1913). “Prepare 1 liter of a dilute 
ammonium-hydroxide solution by adding 3 parts water to 10 parts 
ammonia hydroxide, sp.gr. 0.99. Add a slight excess of copper car- 
bonate and shake vigorously, allow to stand overnight, and then siphon 
off the supernatant solution. Add 15 gms. of unwashed sheet filter 
paper and shake occasionally until the paper is dissolved. Dilute to 
10 liters and add slowly a one to five solution of hydrochloric acid, 
with vigorous shaking until the precipitation of the cellulose is com- 
plete. Dilute to 20 liters, allow the cellulose to settle, and decant the 
supernatant liquid. Wash by repeated changes of water, adding 
hydrochloric acid each time until the copper color disappears; then wash 
with water alone until the solution is free from chlorine. Allow it to 
settle several days and decant off as much of the clear solution as pos- 
sible. If the percentage of cellulose is still too low, a portion of the solu- 
tion is centrifugalized to bring the cellulose content up to 1 per cent.” 
Cellulose solution............... tees 500 c.c 
AQAl.. ee eee teens 10 gms 
Nutrient solution, composed of: 
Potassium phosphate (dibasic)........ 1 gm. 
Magnesium sulphate................. 1 gm. 
Sodium chloride.................0..5- 1 gm. 
. 00 c.c. 
Ammonium sulphate................- 2 gms. 500 ¢.¢ 
Calcium carbonate ................. 2 gms. 
Tap water...........-.. 0 cee eee 1000 c.c. 
