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Potato, 22° C.-Well marked yellow, slimy, shining layer.

Litmus Milk, 37.5° C.-Coagulation of casein, which is redissolved; slight acid reaction.

Broth, 37.5° C.-General turbidity and pellicle formed. Indol reaction slight or absent.

Glucose Formate Broth, 37.5° C.-Grows anäerobically, but no gas produced.

(43) MICROCOCCUS ROSEUS (BUMM).

(Diplococcus roseus, Flügge.) Widely distributed organism, very common in air, frequently present in mouth.

Morphology.—Round, oval and irregular cocci (0.6 to 1.0 u in diameter), often occurring in masses or in pairs.

Staining Reactions.-Stains well with the ordinary aniline dyes and by Gram's method.

Biological Characters.-An äerobic, chromogenic coccus; gelatin slowly liquefied. Not motile ? Micrococcus agilis of Cohn). Grows best at 22° on ordinary media, also at 37.5° C. Pigment only formed in presence of air.

Gelatin Plates, 22° C. Irregular, round or created, raised, small, rose-red colonies on surface, the deep colonies not developing much. The colonies gradually sink into the gelatin. Under { obj., round or lenticular, entire edge, finely granular and pale rose-red in colour.

Gelatin Stab, 22° C.–Fine thread-like growth along stab, gelatin very slowly liquefied. Surface lobed and irregular, rose-red.

Gelatin Shake, 22° C.-Growth of colonies only near surface, little in depths. No gas.

Agar Streak, 37.5° C.-Smooth, shining, regular edge in twentyfour hours. Condensation water clear, and later, with red precipitate. Colour best developed at 20° C.

Potato, 22° C.-Glistening, rose-red, and often with outer white zone, often raised and lobular; medium not coloured.

Litmus Milk, 37.5° C.—No change.

Broth, 37.5° C.-Slight turbidity, with rose-red precipitate, coherent.

On potato cultures of Micrococcus roseus the colonies are a much brighter red.

A number of other cocci producing a red pigment have been described, but they are all apparently related to the Micrococcus roseus. Micrococcus lactericeus (Freund, Cent. für Bakt., Bd. xxi., 834) differs slightly, but is probably a variety. Bacillus roseus (Trans. Odont. Soc., June, 1898) is probably the same; the bacilli were very small and much resembled cocci.

The Sarcina roseus is thought by Lehmann and Neumann to be a "form" of the Micrococcus roseus (for further particulars see Lehmann and Neumann, p. 192).

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APPENDIX.

The Microscope. For bacteriological work'a good compound microscope is necessary and should be fitted with the following:

Objectives.- , t, and 1 oil immersion.
Substage condenser. ---Abbé or other pattern.
Nose piece.
Coarse and fine adjustment.
Mechanical stage.

The microscope consists of several parts which will be considered separately.

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The Stand.—The pattern of stand is not of great importance, but the “ tripod” is the most convenient for general work. It is most important that the stand be rigid and should allow of the body being tilted as far as the horizontal position in stable equilibrium.

The Stage.Two species of stage are in use : (a) the plain, (6) the mechanical ; and for bacteriological work the latter is preferable, but not absolutely necessary. Those mechanical stages which are fixed by screws to the ordinary plain stage rarely work well for any length of time without developing a “kick," thereby throwing the object out of focus whenever the stage is adjusted. In selecting a stage care should be taken to observe that the movement in both directions is free from kick, and moreover sufficient to allow of plate cultivations, &c., being examined. This refers also to the plain stage.

The Substage Condenser.- Various forms of condenser are in use. The Abbé consists of a plano-convex and a concavo-convex lens and is the one generally in use. By means of the condenser the light is focussed upon the object, otherwise stained preparations cannot be brought sharply into focus when the 1. obj. is in use. The condenser should be fitted with an iris diaphragm to regulate the light.

The Mirror.-Should have both plane and convex surfaces. The plane surface is to be used with the condenser.

Body Tube.--This tube carries the objectives and the eye-piece. The continental microscopes have a short body tube, the British a long tube, and the objectives are severally adapted. The body tube should be capable of extension, but it is essential to have a rack and pinion adjustment.

Focusing Adjustments.—The coarse adjustment is essential for all bacteriological work; by its action the objective is lowered till almost in focus and the focusing then completed with the fine adjustment. There are several forms of fine adjustments, and one should be chosen which does not carry more than half the weight of the body tube (see fig. 74).

The Objectives.—The obj. should give a perfectly flat field and sharp definition. The 1 oil immersion lens should give good central definition with no blurring; the edges of the field must be free from colour refraction. The lens should also allow of the diaphragm to be opened to its full extent without causing any blurring of the image.

Great care is necessary in selecting lenses as it is impossible to make all lenses of uniform standard. Diatoms are not entirely satisfactory in testing a lens; blood films stained with eosin and bacteria stained with fuchsin give much better tests.

The oil should always be wiped off the 1g after use with a clean piece of wash-leather kept for the purpose. If any dirt has been allowed to collect on the field lens it is best to clean it off with some immersion oil and the leather.

Only gross carelessness will account for canada balsam upon the 1, and very great care must be exercised in removing it, otherwise the lens cement may be dissolved and the objective ruined.

Eye Pieces.—A low and high power eye-piece are convenient, the former magnifying about 5 diameters, the latter about 12.

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NOTES ON THE USE OF THE MICROSCOPE. (1) Unstained Specimens, Hanging Drop Slides, &c.—Use the 1 first always; it generally gives sufficient magnification for the purpose. Rack the lens down with the coarse adjustment until it almost, but not quite, touches the coverslip, then while looking through the microscope rack upwards until the object comes into view, then proceed with the fine adjustment. When using the condenser the flat side of the mirror should be employed, and with the ; obj. the condenser requires lowering.

(2) Stained Specimens.-Use the i obj., taking care that no canada balsam is on the surface of the coverslip. Place a drop of immersion oil (cedar wood) in the middle of the coverslip, and with the coarse adjustment lower the lens till it touches the oil and all but touches the glass, then looking through the microscope

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