. A text-book upon the pathogenic Bacteria and Protozoa for students of medicine and physicians. Bacteriology; Pathogenic bacteria; Protozoa. Cultures upon Potatoes 213 fortably heated room, not subject to excessive variations, such as are caused by steam heat and the burning of gas, etc., is about the most appropriate. Like the colonies, the cultures must be care- fully examined from day to day, as it not infrequently happens that a growth which shows no signs of liquefaction to-day may begin to liquefy to-morrow or a week hence, or even as late as two weeks hence. The Stroke Culture.—In most
. A text-book upon the pathogenic Bacteria and Protozoa for students of medicine and physicians. Bacteriology; Pathogenic bacteria; Protozoa. Cultures upon Potatoes 213 fortably heated room, not subject to excessive variations, such as are caused by steam heat and the burning of gas, etc., is about the most appropriate. Like the colonies, the cultures must be care- fully examined from day to day, as it not infrequently happens that a growth which shows no signs of liquefaction to-day may begin to liquefy to-morrow or a week hence, or even as late as two weeks hence. The Stroke Culture.—In most cases, the culture is planted by a simple stroke made from the bottom of the tube in which agar- agar blood serum, or other solid medium has been obliquely solidified, and where it is fresh and moist, to the upper part, where it is thin and dry. In addition to this, it is advisable to make a puncture from the center of the obUque surface to the bottom of the tube. This enables us to tell whether the bacteria can grow as readily below the surface as above. Some workers always make a zigzag stroke upon the surface of the agar-agar. This does not seem to have any par-. Fig. S3.—Types of streak cultures: i, Filiform (B. coli); 2, echinulate (Bact. acidi-lactici); 3, beaded (Str. pyogenes); 4, effuse (B. vulgaris); 5, arborescent (B. mycoides) (Frost). ticular advantage except in cases where it is desired to scatter the transplanted organisms as much as possible, in order that a large bacterial mass may be secured. * Stroke cultures upon agar-agar have the advantage that the cultures may be kept in the incubating oven. The colorless or almost colorless condition of the preparation also aids in the detection of chromogenesis. The growth may be filamentous, or simply a smooth, shining band. Occasionally the bacterium does not grow upon agar-agar unless glycerin be added (tubercle bacillus); sometimes it will not grow even then (gonococcus). Cultures upon Blood-serum.'—Bacteria
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