. A text-book upon the pathogenic Bacteria and Protozoa for students of medicine and physicians. Bacteriology; Pathogenic bacteria; Protozoa. 148 Methods of Observing Micro-organisms The best way to examine living micro-organisms is in what is called the hanging drop. A hollow-ground slide is used, and with the aid of a small camel's-hair pencil a ring of vaselin is drawn on the slide about, not in, the concavity. A drop of the material to be examined is placed in the center of a large clean cover-glass and then placed upon the slide so that the drop hangs in the concavity, but does not touch
. A text-book upon the pathogenic Bacteria and Protozoa for students of medicine and physicians. Bacteriology; Pathogenic bacteria; Protozoa. 148 Methods of Observing Micro-organisms The best way to examine living micro-organisms is in what is called the hanging drop. A hollow-ground slide is used, and with the aid of a small camel's-hair pencil a ring of vaselin is drawn on the slide about, not in, the concavity. A drop of the material to be examined is placed in the center of a large clean cover-glass and then placed upon the slide so that the drop hangs in the concavity, but does not touch the glass. The micro-organisms are thus her- metically sealed in an air chamber, and appear under almost the same conditions as in the culture. Such a specimen may be k^t and examined from day to day, the bacteria continuing to live until the oxygen or nutriment is exhausted. By means of a special ap- paratus in which the microscope is placed, the growing bacteria may be watched at any temperature, and exact observations made. The hanging drop should always be examined at the edge, as the center is too thick. In such a specimen it is possible to determine the shape, size,. Fig. 25.—The "hanging drop" seen from above and in profile. grouping, division, sporulation, and motility of the organism under observation. Care should be exercised to use a rather small drop, especially for the detection of motility, as a large one vibrates and masks the motility of the sluggish forms. When the bacteria to be observed are in solid or semi-solid culture, a small quantity of the culture should be mixed in a drop of sterile bouillon or other iiuid. For observing the growth of bacteria where it is desirable to prevent movement, Hill* has invented an ingenious device which he calls the "hanging block" His directions for preparing it are as follows: " Pour melted nutrient agar into a Petri dish to the depth of about one-eighth or one-quarter inch. Cool this agar, and cu
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbacteri, bookyear1919
