Text-book of histology : including the microscopic technic / by Philipp Stöhr ; translated from the tenth German edition by Emma L. Bilstein ; edited, with additions by Alfred Schaper.

  • Philipp Stöhr
Date:
1904
Catalogue details

Licence: In copyright

Credit: Text-book of histology : including the microscopic technic / by Philipp Stöhr ; translated from the tenth German edition by Emma L. Bilstein ; edited, with additions by Alfred Schaper. Source: Wellcome Collection.

    62/496
    MEASUREMENT. ]^or this purpose an ocular-micrometer and stage-micrometer are used. The latter is laid on the stage of a microscope provided with an ocular-micrometer and the number of divisions of the ocular-micrometer corresponding to one part of the stage-micrometer is ascertained.f The dimensions of the spaces of the stage-micrometer being known the size of the object, which with a given magnification will occupy one or more of the divisions of the ocular-micrometer, is easily calculated. The follow- ing illustrations may render the manipulation intelligible. With ocular I and draw-tube pushed in 5 divisions of the ocular- micrometer correspond with one division of the stage-micrometer. Each division of the stage-micrometer used = mm. Hence 5 divisions of the ocular-micrometer = ^ (0.05 mm.), and 1 division of the ocular- micrometer = 0.01 mm. If then any microscopic object, e. g.t a striated muscle-fiber, the diameter of which is to be measured with this magnifica- tion, occupies 4 divisions the fiber is 0.04 mm. broad. It is often difficult, especially with low magnification, to count the fine divisions of the ocular-micrometer. This can be more easily done by noting the longer lines marking every fifth or tenth division. For in- stance, with Leitz Objective 3, Ocular I, and the draw-tube drawn out, 40 divisions of the ocular-micrometer correspond with 5 divisions of the stage-micrometer. Therefore, 40 divisions = mm. = 0.25 mm., and one division of the ocular-micrometer with this magnification = 0.0062 mm., 2 divisions = 0.0124 mm., and so on. With Leitz Objective 7, Ocular I, and draw-tube pushed in, 30 divi- sions of the ocular-micrometer correspond with one division of the stage- micrometer ; 30 divisions = 0.05 mm., one division = 0.0017 mm., or 17/^.J Finally, with Leitz Objective 7, Ocular I, and draw-tube drawn out, 40 divisions of the ocular-micrometer — one division of the stage- micrometer. Therefore, 40 divisions = 0.05 mm., one division = 0.0012 mm., or 1.2 (i. *Some ocular-micrometers (Leitz) are made to rest upon the diaphragm inside the ocular; others (Seibert) to be inserted through a lateral opening; or, in some cases, special oculars (Zeiss) for measuring are made for the microscope. The actual size of the divisions of the ocular-micrometer need not be known. The stage-micrometer is a glass slide on which I mm. with 100 divisions is engraved. Instead of this a second ocular-micrometer, which usually contains a mm. with only 20 divisions, may be used. Measurements made with this are not as accurate, but the errors are so insignificant that they scarcely need consideration. ■f Beginners often find it difficult to focus the lines on the stage-micrometer ; faint or oblique illumination of the object malces it easier to detect them. t One micron = fj — 0.001 mm.
    digitised image 1
    digitised image 2
    digitised image 3