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. 



9. 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 nig. 



1 1 . Same, with the carbon compound changed, e. g. , with sodium formate substi- 

 tuted for sodium acetate. Sodium formate and phenol phthalein 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 Omelianski). 



12. Nutrient starch-jelly for study of diastasic action. (SeeProc.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 a-re 

 then soaked for 45 minutes in I :iooo 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 tine 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-t>ox 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. 



