MICROSCOPY. 461 MICROTASIMETER. hang together iu culjes of eijrht, sixteen, thirty- two, etc., occur in exactly opposite gastric con- ditions, i.e. where hydrochloric acid is present and lactic acid is absent. Yeasts, molds, and leptothri.x are also found. Serous exudates usually show little of diag- nostic import. After standing or after centri- fuging, the sediment may show some epithelial cells, red blood cells, leucocytes, fat globules, cholestorin crystals, etc. Bacteria, if present, are usually in such small numbers as to ro(|uire culture for their recognition. Fairly frequently, however, the gonococcus may be found in the exudate of gonorrhceal arthritis, by simply stain- ing tlie sediment. Less frequently the tu- bercle bacillus may be identified in a similar manner. Purulent exudates when examined under the microscope show large numbers of pus cells which are mainly polynuclear leucocytes. Red blood cells and exfoliated epithelium are also often present. Of bacteria may be mentioned the tubercle bacillus, the bacillus of anthrax, the diphtheria bacillus, the streptococcus, sta- pliylococcus, gonococcus, and pneumoeoccus. For methods of examining for tubercle bacillus, see article on Tubebculosis ; for streptococcus, and stapliylococcus, see article on Bacteria; for pneumoeoccus, see Pneumo.nia. The diphtheria or Klebs-Loeffler bacillus may i)e found in sputum. For examination it is usually, however, obtained directly from the sus- pected membrane. See Diphtheria. Leptothrix and Oidium albicans are organisms sometimes found in exudates associated with dis- eases of the mouth and pharynx. The former is not infrequently the apparent cause of very ob- stinate pharyngitis, while the latter is found in connection with the disease known as thrush. Tissues axd Orgaxs. The examination of pieces of tissue or of organs for the purpose of determining the nature of the disease affecting them is often of great importance. Some tissues may be examined in the fresh state by simply teasing apart in such an inert lluid as normal saline solution (three-quarters per cent, aqueous solution of sodium chloride). The satisfactory examination of most tissues re- quires, however, a more or less elaborate prelimi- nary preparation. This consists in ( 1 ) fixing, (2) hardening, (.3) imbedding, (4) section cut- ting, (5) staining, and (fl) mounting. ( 1 ) Fixing. — This consists in placing the tis- sue, as soon as possible after its removal, in a .solution which will kill the tissue elements rap- idly so that they retain the same form and structure that they had during life. Of the most commonly used fixing agents may be men- tioned alcohol; formalin, in aqueous solutions of from 2<2 to 10 per cent. ; and Miiller's fluid ( potassiinn dichromate, 2.5 grams; sodium sul- jiliate, 1 gram; water, 100 o. c). (2) nardrning and Preserving. — .fter fixing, tissues are usually thoroughly washed in run- ning water and then hardened in graded alcohols, i.e. first in .50 per cent., then in (iO per cent., then in 80 per cent. For permanent preservation they are usually left in 80 per cent, alcohol. (3) Imbedding. — This is for the purpose of impregnating the tissues with some substance which will hold them together during the subse- quent manipulations. The now most commonly employed imbedding mass is celloi<lin, although for special purposes parallin is used. (4) Section Cutting. — This is now accom- plished by means of an instrument known as a microtome. While many of these instruments are quite complicated, the purpose of them all is to carry a knife through the specimen in such a way that sections of any desired thickness may be obtained. (5) Staining. — Sections may be stained in a great varietj' of ways. For general purposes what is known as "staining double' gives satis- factory pictures. Tliis is accomplished by stain- ing the specimen first in a watery solution of ha-motoxylin and then in an alcoholic solution of eosin. The specimens are ne.xt placed in oil of origanum, which removes the alcohol and ren- ders the sections more transparent ('clearing*). (6) Mounting. — From the oil the section is transferred to a glass slide, the excess of oil re- moved by blotting with filter paper, a drop of Canada balsam placed on the specimen, and the whole covered by means of a cover glass. This makes a permanent mount. For other methods of staining and mounting the reader is referred to special text-books on histology and histological technique. Bibliography. Carpenter, The Microscope and Its Rci-elations (8th ed., Philadelphia, 1901); Lee, TIte Mierotomist's Vadc-Mecutn (5th ed., Philadelphia, 1900) ; Henneguy, ilethodes techniques de Vanaiomie microscopique (Paris, 1887); Sz;v'nionowicz, Lchrbueh der Histologie (Wiirzburg, 1900) ; Dunham, Histology, Normal and Morbid /Philadelphia, 1898) ; Cl'arkson, A Text-Book of Histoloyg (Philadelphia, 1896); Bohm-DavidofT-Huber, Lehrbueh der Histologie dcs Menschen (Wiesbaden, 190.3) ; Stiihr, His- tologie (10th ed., Jena, 1903); Abbott, Princi- ples of Bacteriology (3d ed., Philadelphia, 1895) ; Delafield and Prudden, Pathological Anatomy and Histology (6th ed., Xew York, 1901) ; Nich- ols, Clinical Laboratory Methods (New Y'ork, 1902) ; Peyer, An Atlas on Clinical Microscopy (Xew York, 1885) ; Pellew, Manual of Chemis- try (Xew Y'nrk, 1892). MI'CROSOME (from Gk. iuKp6s, mikros, .small -f- ciifia, soma, body). A name given to minute granules which occur in protoplasm. MI'CROSPORAN'GIUM (NeoLat., from Gk. /uKpis. 7nikros, small -- (rirbpo!, sporos, seed -f dyyctov, angcion, vessel, from S.yyot, angos, jar). The spore-case (sporangium) which produces the microspores. For example, the pol- len sacs of flowering plants are microsporangia. See Heterospory; Sporangium. MI'CROSPORE (from Gk. ^i/opit, mikros, small + cnrSpo!. sporos, .seed). In the higher plants, the smaller of the two kinds of spores produced. They develop the small male plants (male gametophytes) . Pollen grains are micro- spores of flowering plants. See IIeterospoby; Spore. MICROSPOR'OPHYLL (from Gk. /xiKpSt, mikros, small + crirSpoi. sporos. seed -|- <(ivop, phyllon, leaf). In higher plants, the leaf struc- tures (sporophylls) . that bear the microspores, e.g. the stamen of flowering plants. See Hetero- spory; SpoRorini-L. MI'CROTASIMTETER (from Gk. p.iKp6,, mi- kros, small -f riaii, tasis, extension -|- p.(Tpov,
