Lectures on clinical medicine / [John Hughes Bennett].

  • Bennett, John Hughes, 1812-1875.
Date:
1850-1856]
Catalogue details

Licence: Public Domain Mark

Credit: Lectures on clinical medicine / [John Hughes Bennett]. Source: Wellcome Collection.

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    down. This table should always be referred to during the description of objects, and the amount of magnifying power invariably stated. The art of demonstrating under the microscope is only to be acquired by long practice, and, like everything requiring practical skill, cannot be learnt from books or systematic lectures. I can only, therefore, give you very gene¬ ral directions on this head. . . , All that is necessary in examining fluid substances, is to place a drop in e centre of a slip of glass, and letting a smaller and thinner piece of glass fall gently upon it, so as to exclude air bubbles, place it upon the stage under e objective. In this way the fluid substance will be diffused equally over a flat surface, and evaporation prevented, which would dim the objective. The illumination must now be carefully arranged, and the focus obtained, first by means of the coarse, and then by means of the fine, adjustment. . It will save much time, in examining structures, to employ always, at one sitting, the same slips of glass, as it is easier to clean these with a towel, after dipping them m water, than to be perpetually shifting the coarse adjustment. The action of water, acetic acid, and other re-agents on the particles con¬ tained in the fluid, may be observed by adding them to another drop before covering with the upper glass ; or when this is done, a drop of the re-agent may be placed at the edge of the upper glass, when it will be diffused through the fluid under examination by imbibition. The mode of demonstrating solid substances will vary according as they are soft or hard, cellular or fibrous, &c. &c. The structure of a soft tissue such as the kidney, skin, cartilage, &c., is determined by making very minute, thin, and transparent slices of it in various directions, by means of a sharp knife or razor. These sections should be laid upon a slip of glass, then covered over, and slight y pressed flat, by means of an upper one. The addition of a drop of water renders the parts more clear, and facilitates the examination, although it should never be forgotten that most cell-structures are thereby enlarged or altered in shape from endosmosis. Acid and other re-agents may be applied in like manner. The double bladed knife of Valentin will enable you to obtain large, thm, and equable sections of such tissues, and permit you to see the manner in which the various elements they contain are arranged with regard to each other. Harder tissues, such as wood, horn, indurated cuticle, &c., may be examined by small thin sections, made in the same way. Very dense tissues such as bone, teeth, shell, &c., require to be cut into thin sections, and after¬ wards ground down to the necessary thinness. Preparations of. this kind are now manufactured on a large scale, and may be obtained at a trifling cost. A cellular parenchymatous structure, such as the liver, may be examined by crushing a minute portion between two glasses. If it be membranous, as the cuticle of plants, epithelial layers, &c., the membrane should be carefully laid flat upon the lower glass, and covered with an upper one. A fibrous structure, such as the areolar, elastic, muscular, and nervous tissues, must be separated by means of needles, and then spread out into a thin layer before examination, with or without water, &c.