Fig. 51.—A good practical microtome for paraffin and celloidin work. Well-adapted to needs of students and beginners.
Next to the microscope the most important instrument in pathologic work is the microtome. One that can be used for either celloidin or paraffin work, and that can also be utilized as a freezing microtome, should be selected in private work, when economy is desired. The majority can be used for either paraffin or celloidin, and one of the Becker models can be easily attached to the carbonic acid holder for the cutting of frozen material. The Bardeen freezing microtome is relatively inexpensive, very satisfactory, and can be easily attached to the carbonic acid tanks. It can be recommended for freezing work. The “slide” type, either that in which the knife-holder is moved by the hand directly or by a crank turned by the hand, is advised for ordinary diagnostic work. For students and beginners the crank is of great advantage, as the knife is securely held and cannot jump. The best microtomes are made by Schanze of Leipzig, Jung of Heidelberg, Becker of Göttingen, the Cambridge Scientific Co., the International Instrument Co., and the Bausch & Lomb Co. For either celloidin or paraffin work the medium or large Schanze slide-microtome or the Minot’s precision microtome are recommended; for cutting serial sections in paraffin the latest modification of the Minot automatic rotary microtome is especially adapted. The best microtome knives are made by Walb of Heidelberg. A long, heavy knife is to be preferred to a light one. For the freezing microtome a knife of the type of the blade of a carpenter’s plane set in a wooden handle should be used, Hones and strops of the best quality are necessary.
Paraffin-ovens and drying-ovens of suitable size, and constructed preferably of copper, are necessary for paraffin work. The water-space about the oven should be sufficiently large, and the temperature should be controlled by a thermo-regulator. Various models are offered in the trade, but they can be made more cheaply by the local tinsmith. The thermo-regulator can also be home-made by anyone who has the necessary training in glass-blowing usually given in courses in bacteriology.
Various instruments and utensils, such as razors, double-bladed knives, forceps, spatulas, section-lifters, needles, scalpels, scissors, glass rods and tubing, test-tubes, graduates, flasks, funnels, bottles, staining dishes, reagent bottles, rubber tubing, water-bath, tripods, centrifuge, Bunsen burners, asbestos pads, gauze, filter-papers, absorbent paper, labels, oil and wax colored pencils, slides, cover-glasses, slide-boxes, camel’s-hair brushes, glass droppers, platinum wire, etc., are required for the pathologic laboratory, and can be chosen to suit the individual needs. The solid watch glasses make very good small staining dishes; the enamelled trays and glass dishes used in photographic work are especially adapted to the plate-method, particularly the size used for the 4 × 5 plate. Tea-strainers or small sieves can be used for staining a large number of celloidin sections; and there are different types of staining-dishes designed for the staining of slide- and cover-glass preparations in number. Slides should be of the best quality, colorless and with ground edges, and of medium thickness. Cover-glasses should be square or oblong, round covers having but little use in pathology. For ordinary work the No. 2 square, ¾ inch, is recommended; for work with the higher-power dry objectives a thinner cover must be used. Slides and covers may be cleaned by placing them in a solution of equal parts of one per cent sulphuric and chromic acids and then rinsing in distilled water. A good cleaning fluid is also made of one part acetic acid to three of 80 per cent alcohol. To clean old mounts melt the balsam by heat or dissolve in turpentine, separate slides and covers, boil in ten per cent lysol for half an hour, or for ten minutes in the sulphuric-chromic-acid mixture, rinse thoroughly, dry with cloth having no lint.
The laboratory should be supplied with running water, a sink large enough for washing out specimens, numerous stop-cocks, and a drip-board. Distilled water in abundance must be available. The laboratory-table should have an alcohol- and xylol-proof finish, black on the whole being the most practical color. A portion of the table should be covered with glass beneath which there is laid a sheet of white paper.
CHAPTER XVIII.
THE EXAMINATION OF FRESH MATERIAL.
I. METHODS OF EXAMINATION.
Pathologic material is examined in the fresh state when it is desired to make a diagnosis in the shortest time possible, or when the processes of fixation and hardening produce such alterations in the morphology and chemic constitution of the cells that these features can be recognized only in the unfixed, fresh state. So far as the saving of time is concerned it is possible to take material removed during an operation, examine it in the fresh state, and return a diagnosis to the surgeon, while the patient is still on the table under the influence of the anæsthetic. It is not possible to do this with all tissues or with all pathologic conditions; but, when it can be done, the advantages of such a rapid diagnosis, in the saving of time, labor, expense and danger to the patient, are obvious. The best idea of the cell is also gained by its study in a fresh condition. Vital phenomena and certain morphologic features, as cilia, can be observed only in fresh material. Many of the chemic constituents of cells (glycogen, fat, mucin, pseudomucin, albumin-granules, cholesterin, etc.) are either lost, or are so changed by processes of fixation or hardening that they can no longer be recognized. The majority of specific chemic tests can be made in fresh tissues only. Moderate and slight degrees of fatty degeneration and cloudy swelling are easily recognized in the fresh state; in fixed and hardened preparations they may not be recognized at all. Particularly in the case of the heart-muscle is it necessary to make an examination of the fresh material when the diagnosis of these conditions is concerned. Further, a greater or less degree of shrinking is caused by many of the agents used in fixing and hardening, and this is avoided by the examination of the fresh material. In the case of pathologic fluids (sputum, urine, féces, etc.) an examination of the sediment in the fresh state should always be made as a matter of routine. The formed elements of these fluids are best determined by this means. In the case of tissues, a diagnosis made by means of scrapings, smears, teased bits of tissue, frozen sections, etc., should always be controlled by the examination of fixed and hardened material.
In the examination of fresh material the following methods are employed: Sedimentation, smears, scraping, crushing, teasing, maceration, sections, shaking or penciling, digestion, intravital staining, injection, the warm stage and “cultivation.”
1. Sedimentation. The formed elements of pathologic fluids (urine, sputum, pus, blood, exudates, transudates, cyst-contents, etc.) are examined by collecting the sediment of such fluids from the bottom of a sedimenting glass or bottle, by means of a capillary pipette controlled by the finger. While the sediment is passing up into the tube the pipette should be moved about the bottom of the vessel so as to get some of the sediment from all parts. When the fluid is rich in cellular elements sedimentation is not necessary; a drop of the fluid is placed upon the slide; if too thick it is diluted with physiologic salt-solution or serum. If poor in cellular elements the fluid must be centrifugalized by means of a water- or electric-centrifuge; and a drop of the sediment in the centrifuge tube is then removed by the pipette and placed upon the slide, and covered with a cover-glass. To facilitate the low-power examination of such sediments parallel streaks upon the slide may be made across its entire length, and examined without the use of cover-glasses. To apply the various reagents mentioned below it becomes necessary to use a cover-glass as directed.