1. BLOOD. Fresh spots should be scraped off and examined in physiologic salt solution. Older spots are scraped off when possible, or if the spots are on clothing or other fabrics, a piece of the stained portion is cut out, and the scraping or piece of material is placed on a slide in a macerating fluid (30 per cent caustic potash; glycerin 3 parts and concentrated sulphuric acid 1 part; 15 per cent tartaric acid; equal parts alcohol and ether; or Pacini’s fluid [mercuric chloride 1 grm., sodium chloride 2.0 grm., glycerin 100 cc., water 300 cc.]). Even in very old clots or stains some red cells may retain their characteristic form. The process of maceration should be observed directly under the microscope, as the macerating fluid gradually changes the cells after they become loosened. Schmorl advises the following method:—
Moisten a small piece of the fabric in water and stain with hæmatoxylin. Differentiate in acid alcohol, wash thoroughly in water, stain with 1/1000 watery eosin solution, wash in water (3-6 hours), place in alcohol, and then again in water. Tease with great care into fine threads on the slide, and examine the isolated fibres in a drop of glycerin. The red corpuscles are easily recognized; and the nuclei of the white cells or of the red cells of birds and amphibia stand out distinctly. Permanent mounts may be made by passing the specimen through alcohol, xylol, and mounting in balsam. A portion of the stained fabric may be imbedded in celloidin, sections cut, and stained with hæmatoxylin and eosin.
The red cells may be measured by the ocular micrometer. Those of man are somewhat larger than those of other mammals, but the difference in size is so slight that an absolute determination of the source of the blood is not possible from the consideration of size alone. Human corpuscles measure 0.0077 mm. in diameter; the nearest in size are the corpuscles of the dog, rabbit, hog, cow, horse, cat and sheep, in the order given, those of the sheep being smaller. The measurements of a large number of corpuscles must be taken if the question of size is to be considered. When red cells cannot be found the stains must be tested for the presence of blood pigment (Teichmann’s hæmin crystals). A small piece of the scraping or stained fabric is placed upon a slide in glacial acetic acid; the fluid is expressed; and a small crystal of sodium chloride or sodium iodide is added to the fluid. Cover with cover-glass and heat gently until bubbles are given off, and continue carefully until the acetic acid has evaporated. The slower the evaporation the larger the crystals will be. Examine with a ⅙ inch or No. 7 objective. The hæmin crystals are brown or claret-colored, of the shape of rhombic plates single or superimposed. They are insoluble in water, alcohol and ether; dissolve slowly in ammonia, dilute sulphuric and nitric acids, and easily in caustic potash. The form of the crystal and the color determines the diagnosis of the presence of blood, but does not distinguish between human and animal blood. Old stains should be treated with acetic acid 12-24 hours before attempting to obtain the crystals. Contamination of the fabric with fat interferes with the reaction; the fat should be removed first with ether. If the suspected stain occurs on iron, steel, sand, clay or coal, the crystals usually cannot be obtained. Decomposition may also interfere with the reaction. In such cases a solution of the stain in a saturated solution of borax should be made and submitted to spectroscopic examination. The presence of blood-pigment on any substance can be demonstrated by means of the spectroscope or microspectroscope. Within recent years the biologic test for blood and albumins has been turned to medicolegal uses, in the differential diagnosis of human and animal blood or albumins. This test rests upon the principle that in the serum of an animal treated with human blood or albumin there are developed antibodies having a strong specific hæmolytic or precipitating action upon human blood or albumin.
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.
Hairs of the beard are usually thickest (0.14-0.15 mm. in diameter), then follow in order of size the pubic hairs of the female, the hairs of the eye-lids, male pubis, male head, and female head (0.06 mm. in diameter). There are, however, marked individual differences, and the hair of infants is much finer than that of older children and adults. The hairs of the new-born are pointed, as are also the hairs of adults that are protected from cutting, rubbing, maceration, etc. Cut hairs are at first blunt; later more rounded. Hairs that have been torn out usually show a bulbous end with the remains of the hair-follicle; fallen hairs have a closed, smooth, atrophic root. When the question arises as to the definite individual from whom certain hairs may have come a very careful comparison of the given hairs with those of the individual concerned must be carried out, as to color, size, thickness of different layers, shape and size of the transverse section, etc. Paraffin imbedding should be employed for this purpose.