2. =Semen.= Suspected seminal stains may be tested first by the =Florence sperm reaction=. A portion of the material is mixed on the slide with a drop of an iodine solution (1.65 iodine, 2.54 potassium iodide, 30 water). Cover and examine with low power. The formation of characteristic long rhombic, brown or violet crystals is evidence of the presence of semen. The reaction is hindered by decomposition. The =spermatozoa= may also be demonstrated in seminal stains by soaking the fabric, carefully flattened out, in a watch-glass containing dilute hydrochloric acid (1 drop to 40 cc. distilled water), for 5 minutes to 5 hours, according to the age of the stain. The fabric is then removed and gently rubbed on a slide; the smear is covered with a No. 1 cover-slip, and examined with the oil immersion or the highest dry objectives. The smear may be stained by adding neutral red solution to the macerating fluid, or by drying the smear in the air, fixing in the flame, and staining with hæmatoxylin and eosin, neutral carmine or fuchsin. The staining and macerating solutions may be combined in one. The piece of fabric containing the suspected seminal stain is soaked in a mixture of methyl green 1 grm., hydrochloric acid 15 drops, distilled water 350 cc., for 1-6 hours. It is then removed with the forceps and smeared on the slide, examined in the moist state, or dried, fixed and mounted. The head is stained an intense green. 3. =Decidua and Foetal Tissues.= Clots, curettings and discharges may be examined in the fresh state by teasing; or the material may be fixed in formol, formol-Müller’s or mercuric chloride. The characteristic structures of the decidual cells, chorionic villi and other fœtal tissues are easily recognized and the presence of any one of these determines the occurrence of pregnancy, abortion or child-birth. 4. =Hair.= The most important medicolegal question concerning hair is the differential diagnosis between animal and human. The following points must be considered:— _1._ The cells of the outer layer (cuticle) of the hair are much larger in the majority of animals than in man, and are much more distinctly seen. The cuticle is much more dentate or serrate in the hair of animals than in that of man. _2._ The cortical layer in human hair is much thicker than in animal hairs, as compared to the thickness of the medulla; in animal hair the medulla is thicker than the cortical layer. _3._ The cellular structure of the medullary substance is indistinct in human hair; in animal hair it is very prominent. In human hair the medulla is often absent, especially in certain portions of the hair, while in animals it is rarely absent, and then only in sharply localized portions. The hair should always be examined throughout its entire length.