The micro-organisms of fermentation practically considered / by Alfred Jörgensen.

  • Jörgensen, Alfred, 1848-1925.
Date:
1889
Catalogue details

Licence: Public Domain Mark

Credit: The micro-organisms of fermentation practically considered / by Alfred Jörgensen. Source: Wellcome Collection.

    46/198 (page 24)
    known thickness (0-2 mm., for instance) is cemented, and wliich lias a circle cut out of its centre. Fig. 6.—H.'ematimeter. a, glass slide ; b, cemented cover-glass with circular opening ; c, cover- glass. A small drop of the liquid containing the cells is brought into tbis bollow, a cover-glass is placed over the opening, and rests on the cemented, perforated cover-glass. The drop of the liquid must not be so large that this pressure causes it to flow out from the cut-out space enclosed; it must, however, be high enough to be in contact with the superincumbent cover-glass. The thickness of the layer of the liquid is then known. In order to determine the other two dimensions, and thus be able to work with a given volume of liquid, one of the generally Imown micro- meters, consisting of a thin piece of glass on which a number of small squares are engraved, is brought into the eye-piece of the microscope. The actual value of each of these squares is known when a given System of lenses is employed, and, therefore, when the square is projected on the object, a small prism of known volume is defined. In certain cases it is more useful to have a fine System of small squares of known diameter engraved on the glass slide itself at the bottom of the cavity (Zeiss, of Jena, has made a chamber of this sort from the instructions of Professor Thoma) ; this also improves the microscopic definition of the cells which are on the bottom of the chamber. When only a determination of the multiplying capacity of the cells is desired, or repeated observations of the number of cells in the same volume of liquid, it is quite superfluous