Florence's Reaction.--The suspected material is softened with water, placed upon a slide with a few drops of the reagent, and examined at once with a medium power of the microscope. If the material be semen, there will be found dark-brown crystals (Fig. 131) in the form of rhombic platelets resembling hemin crystals, or of needles often grouped in clusters. These crystals can {285} also be obtained from crushed insects, watery extracts of various internal organs, and certain other substances, so that they are not absolute proof of the presence of semen. Negative results, upon the other hand, are conclusive, even when the semen is many years old. The reagent consists of iodin, 2.54 gm.; potassium iodid, 1.65 gm.; and distilled water, 30 c.c. {286} APPENDIX I. APPARATUS AND REAGENTS The apparatus and reagents listed here are sufficient for all the tests described in the text. Those in smaller type are less frequently required. For ordinary routine work a much smaller list will suffice. A. APPARATUS Beakers and flasks, several sizes, preferably of Jena glass. Blood lancet, or some substitute (Fig. 64). Bunsen-burner or alcohol lamp. Buret, 25 c.c. capacity; preferably with Schellbach stripe. Buret and filter-stand combined. Centrifuge--hand, electric, or water-power (Figs. 16 and 17). With the last two a speed indicator is desirable. Radius of arm when in motion should be six and three-fourth inches. Plain and graduated tubes accompany the instrument; milk-tubes (Fig. 128) must be purchased separately. When sedimentation only is desired, the torfuge (Fig. 31) is a cheap and convenient substitute. Cigaret-paper, "Zig-zig" brand, or some similar thin paper. Corks, preferably of rubber, with one and two holes. Cover-glasses, No. 2 thickness--seven-eighth-inch squares are most convenient. {287} Cover-glass forceps. Esbach's tube (Fig. 23). Evaporating dish. Filter-paper: ordinary cheap paper for urine filtration; "ashless" quantitative filter-paper for chemic analyses. Glass funnels. Glass rods and tubing of sodium glass: for stirring rods, urinary pipets, etc. Glass slides: the standard 1- by 3-inch size will answer for all work, although a few larger slides will be found convenient; those of medium thickness are preferable. Graduates, cylindric form, several sizes. Granite-ware basin. Hemoglobinometer: see pp. 143 to 147 for descriptions of the different instruments. Hemocytometer: either Türk or Zappert ruling is desirable (Figs. 69, 70, and 72). Labels for slides and bottles. Litmus paper, red and blue, Squibb's preferred. Microscope (Fig. 1): should have Abbé condenser, 1- and 2-inch eye-pieces, and two-thirds, one-fifth, or long focus one-sixth and one-twelfth inch objectives. A one-half inch eye-piece, a micrometer eye-piece, and an attachable mechanical stage are very useful additions. Petri dish or cleaned photographic plates for sputum examination. Stomach-tube.