. A laboratory guide in elementary bacteriology. Bacteriology. 34 General Bacteriology. Inasmuch as the first plate is invariably too thickly seeded to be of much service, this gelatin tube is often replaced by a water blank, which is treated exactly as the gela- tin tube No. 1, but is not of course "plated" but simply serves to dilute the material. References. A. 124; H. 57; L. & K. 88; M. & W. 108; M. & R. 61; McF. 140; N. 171; P. 224; S. 72. Special Directions. a. Make three gelatin plate cultures, as directed above, and inoculate with B. sub- tilis, introducing a minu
. A laboratory guide in elementary bacteriology. Bacteriology. 34 General Bacteriology. Inasmuch as the first plate is invariably too thickly seeded to be of much service, this gelatin tube is often replaced by a water blank, which is treated exactly as the gela- tin tube No. 1, but is not of course "plated" but simply serves to dilute the material. References. A. 124; H. 57; L. & K. 88; M. & W. 108; M. & R. 61; McF. 140; N. 171; P. 224; S. 72. Special Directions. a. Make three gelatin plate cultures, as directed above, and inoculate with B. sub- tilis, introducing a minute portion of agar culture (XIII) into tube No. 1, two loops of No. 1 into No. 2, and three of No. 2 into No. 3. Label, and when the gelatin has solidi- fied, place plates in cool chamber (XV). b. Also make a "blank" plate from an uninoculated gelatin tube, observing all pre- cautions to prevent contamination. This will serve as a control or check on your other plates. If any colonies develop on this it indicates carelessness. EXERCISE XXVII. AGAR PLATE CULTURES. General Directions. These are made in the same way as the gelatin plates ex- cept that the high melting point (96° C.) of agar makes it necessary to use boiling water to melt it. Inasmuch as the vitality of vegetative bacteria is destroyed at a temperature much above 42° C, it must be cooled down before inoculating, but as agar solidifies at 39-40° C. it must not, therefore, be cooled below that point. It is best to keep the melted agar at about 42° C. for 10 minutes before it is inoculated. For this purpose a water- bath should be so arranged that the temperature can be controlled by means of a thermo-regulator. A cheap and yet satisfactory arrangement is represented in Fig. 11. Inoculate, make dilu- tions and pour as in case of gelatin, except that before the agar is poured, it is well to slightly warm the Petri dishes by placing them in the incubator at 38° C. for a few minutes, other- wise the agar m
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