50 BACTERIA IN RELATION TO PLANT DISEASES. 
6. Uschinsky’s solution with various carbon compounds substituted for the 
glycerin (fermentation tubes). 
7. Fraenkel and Voge’s solution. 
8. Raulin’s solution. 
g. Fermi’s solution. 
10. Water (distilled), 1,000,ooomg.; dipotassium phosphate, 2,000 mg.; ammonium 
phosphate, 100 mg.; magnesium sulphate, 100 mg.; sodium acetate, 5,000 mg. 
11. Same, with the carbon compound changed, e. g., with sodium formate substi- 
tuted for sodium acetate. Sodium formate and phenolphthalein may be added also 
to bouillon or agar (2 per cent) for observations during the early stages of growth, 
some organisms reddening this medium promptly by decomposition of the sodium salt. 
(See a recent paper by Omélianski). 
12. Nutrient starch-jelly for study of diastasic action. (See Proc. Am. Asso. Adv. 
Sci., 1898, p. 411, or Centralb. f. Bakt., 2te Abt., Bd. V., p. 102.) 
One gram of starch is rubbed up with a sterile glass rod in 10 cc. of the sterile nutrient fluid 
(Uschinsky’s solution, etc.), placed in a slanting position, in test-tubes, and solidified in a blood- 
serum oven (fig. 45) or in the top of a steamer with the vents left open. There should be several 
heatings of two hours each to insure sterilization. The temperature should not exceed 93° C. nor 
fall much below 85° C. Sterilization is rendered much easier if the starch is prepared in a cleanly 
way. The only difficulty the writer has experienced is in the formation of a thin film of semi- 
opaque solidified starch on the walls of the tubes above the slant. This often cracks off, however, 
during the heatings, and is largely obviated by placing the tubes in a slanting position before the 
starch is rubbed up in the fluid, taking care to soil the walls above the slant. surface as little as 
possible during the operation. The potato-starch is prepared as follows: 
One-half bushel of large smooth potatoes are scrubbed, and the black specks dug out; they are 
then soaked for 45 minutes in 1:1000 mercuric-chloride water. Meanwhile the hands are scrubbed 
clean and given a five minutes washing in the mercuric-chloride water. The tubers are now rinsed 
in sterile water, pared deeply, grated as for potato-broth, and thrown into beakers containing sev- 
eral liters of distilled water, where the pulp is worked over with the hands to liberate as much 
starch as possible. The starchy water is now removed from the pulp by passing it through several 
folds of surgeon’s gauze, squeezing out of the pulp as much of the fluid as possible. When the 
starch has settled the brownish fluid and floating fragments are poured off or decanted, and 
fresh distilled water is added. The smaller fragments of cell-wall, etc., are then removed by forc- 
ing the starch (stirred up in water) through a moderately fine-meshed towel (not too fine) with 
gentle hand-rubbing, into another beaker. Most of the medium-sized and finer starch-grains pass 
through, leaving in the towel the coarser grains and those fragments of cell-wall which passed 
through the coarser meshes of the surgeon’s gauze. The purified starch is now allowed to stand 
for about a week in the ice-box in distilled water (3 liters or more per beaker or jar), The water 
is siphoned off twice a day at first, and afterwards once a day, the starch being stirred up thor- 
oughly every time fresh water is added. Finally the starch is drained very free from water, scooped 
out with sterile spoons or spatulas, placed in uncovered sterile Petri dishes, and dried in the 
blood-serum oven at 56° C., the cover being raised an inch (on corks) to let the moisture out. 
One-half bushel of sound potatoes should yield from 400 to 500 grams of air-dry aseptic starch. 
Potato starch has been selected because it is easy to prepare, but other starches might yield in- 
teresting results. Bacteriologists now pay great attention to the fermentation of sugars, but thus far 
very little consideration has been given to the action of bacteria on starches and celluloses. What- 
ever starches are used, they should be prepared in the laboratory, under aseptic conditions, so as to 
exclude spore-bearing organisms. 
13. Starch-jelly with ‘addition of various sugars, gums, and alcohols (for study 
of organisms having little or no action on starch). 
14. Tubes of slant nutrient agar (+ 15 of Fuller’s scale) with varying amounts 
of c. p. glycerin, 2 to 10 per cent or more. 
