The microscope and histology / by Simon Henry Gage ... pt. I. The microscope and microscopical methods.

  • Gage, Simon Henry, 1851-1944.
Date:
1892
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Licence: Public Domain Mark

Credit: The microscope and histology / by Simon Henry Gage ... pt. I. The microscope and microscopical methods. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

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    would best be very transparent. That is, tissues, fibers, etc., should be mounted in balsam (Suffolk). \ 156. Purpose of a Micro-Polariscope.—The object of a micro-polariscope is to determine, in microscopic masses, one or more of the following points: (A) Whether the body is singly refractive, mono-refringent or isotropic, that is opti- cally homogeneous, as is glass and crystals belonging to the cubical system ; (B) Whether the object is doubly refractive, birefringent or anisotropic, uniaxial or bi- axial ; (C) Pleochromism ; (D) The rotation of the plane of polarization, as with solutions of sugar, etc. ; (E) To aid in petrology and mineralogy ; (F) To aid in the determination of very minute quantities of crystallizable substances ; (G) For the production of colors. For penological and miueralogical investigations the stage of the microscope should possess a graduated rotating stage so that the object can be rotated and the exact angle of rotation determined. It is also found of advantage in investigating objects with polarized light where colors appear, to combine a polariscope and spectroscope (Spectro-Polariscope). MICRO-POLARISCOPE—EXPERIMENTS. § 157. Arrange the polarizer and analyzer as directed above (§ 152) and use an 18 mm. objective except when otherwise directed. (A) Isotropic or Singly Refractive Objects.—Light the micro- scope well and cross the Nicols, shade the stage and make the field as dark as possible (§ 151). As an isotropic substance, put an ordinary glass slide under the microscope. The field will remain dark. As an example of a crystal belonging to the cubical system and hence iso- tropic, make a strong solution of common salt (sodium chloride Na CI.), put a drop on a slide and allow it to crystallize, put it under the micro- scope, remove the analyzer, focus the crystals and then replace the an- alyzer and cross the Nicols- The field and the crystals will remain dark. (B) Anisotropic or Doubly Refracting Objects.—Make a fresh preparation of carbonate of lime crystals like that described for pedesis (§ 95). or use a preparation in which the crystals have dried to the slide, use a 5 or 3 mm. objective, shade the object well, remove the an- alyzer and focus the crystals, then replace the analyzer. Cross the Nicols. In the dark field will be seen multitudes of shining crystals, and if the preparation is a fresh one in water, part of the smaller crys- tals will alternately flash and disappear. By observing carefully, some of the larger crystals will be found to remain dark with crossed Nicols, oth- ers will shine continuously. This shows that the crystals are uniaxial. If the crystals are in such a position that the light passes through them par- allel with the principal axis, the crystals are isotropic like the salt crys- tal and remain dark. If, however, the light traverses them in any other direction the ray from the polarizer is divided into two constitu- ents vibrating in planes at right angles to each other, and one of these