Forensic Medical Tests

FORENSIC MEDICAL TESTS, investigations of various kinds used in forensic medical practice during autopsies and the examination of material evidence. In forensic medical examinations of a corpse, in cases where there are indications of poisoning, tests for certain poisons can be performed right at the corpse. They are very simple to perform, require a limited number of reagents without the use of complex instruments (test for mercury with a copper plate, a coin with organs, e.g., liver (formation of amalgam)). Such tests are used to detect salts of mercury, arsenic, hydrocyanic acid, carbon monoxide, and certain other less frequently encountered poisons (copper, phosphorus). Tests for mercury. Reinsch's test (Marsh). Stomach contents or vomit are placed in a small vessel and acidified with HCl to a clearly acidic reaction. A clean copper plate is lowered into the vessel's contents and heated. The presence of mercury is recognized by a grayish dull coating on the plate, which after light friction acquires a silvery mirror appearance (amalgam). Placed in a narrow test tube, the plate with the coating gives a grayish coating on the glass in the cold part of the test tube upon heating. Upon microscopic examination, the coating consists of microscopic globules of mercury. The plate and the mercury coating in the tube can be left as corpus delicti. A copper plate or copper coin can be placed on the gastric mucosa or sliced liver. In the presence of mercury salts, a grayish coating appears on them. Tests for arsenic. 1) Reinsch's test is performed in the same way as for mercury, using a copper plate on which arsenic gives a grayish coating. When the plate is heated in a narrow test tube, arsenic gives a coating of microscopic crystals in the form of regular octahedra and tetrahedra. 2) If during an autopsy whitish grains of arsenious acid are found in the stomach, Berzelius's test can be performed. In a hard-glass tube sealed at one end with a drawn-out narrow blind cone, 1-2 found grains are placed and a small piece of charcoal (charred stick or match) is inserted from above, which should fit rather tightly into the narrow end of the tube. The tube at the place where the charcoal is located is heated on an alcohol burner so that the charcoal becomes red-hot, then the bottom of the tube with the grains is heated. The vapors of arsenious acid, after passing through the red-hot charcoal, settle on the cold parts of the tube, forming a mirror coating of arsenic. The narrow end of the tube can be sawed off, and the mirror coating in the sealed tube left as corpus delicti. Tests for hydrocyanic acid. 1) A little heart blood is poured into a test tube. A drop of AgNO₃ solution is placed on a glass slide and covered with the test tube, drop down. From the presence of even traces of hydrocyanic acid, the drop becomes milk-white. Microscopic examination reveals the presence of needle-shaped crystals of silver cyanide. 2) Filter paper moistened with a fresh 3-5% alcoholic solution of guaiac resin and then with a CuSO₄ solution (1:1,000) turns blue if placed over a mass containing hydrocyanic acid (over an opened corpse, stomach contents, etc.). Tests for carbon monoxide. 1) Hoppe-Seyler's soda test. A few drops of blood are mixed on a porcelain plate or in a test tube with a few drops of NaOH (10-20%). Blood containing carboxyhemoglobin takes on a brick-red hue, and in its absence, a greenish-brown one. 2) Spectral analysis (see Carbon monoxide, detection in forensic cases) reveals the presence of two absorption bands in the yellow-green part of the spectrum, which do not change upon the addition of ammonium sulfide (distinction from the oxyhemoglobin spectrum). In poisoning with ammonia (ammonia water), the following test can be performed: a glass rod moistened with concentrated hydrochloric acid is brought near the stomach. In the presence of ammonia, white vapors of ammonium chloride are formed. In poisonings with morphine or strychnine, crystals of these alkaloids can sometimes be detected in the oral cavity or on the gastric mucosa. Corresponding tests for alkaloids can be performed with the found crystals. Preliminary tests for poisons do not in any case preclude a forensic chemical investigation of internal organs. In the examination of material evidence, tests for the presence of blood and semen are used. Tests for the presence of blood are subdivided into preliminary and those proving the presence of blood on the object under study. Preliminary tests for blood. 1) Van Deen's test (see Guaiac test). 2) Hydrogen peroxide test (Schönbein). 1-2 drops of a fresh 1-3% hydrogen peroxide solution are applied to the surface of the blood stain. Soon, a foam of small bubbles appears on the surface of the stain due to the release of oxygen. Some authors suggest spraying hydrogen peroxide from an atomizer. This is especially convenient to perform on objects where it is difficult to find suspicious stains, e.g., on dark fabrics, the appearance of bubbles can indicate the place that should be subjected to further study. 3) Phenolphthalein test (Meyer's). The reagent is prepared: 2 g of phenolphthalein, 20 g of KOH, and 10 g of zinc dust are boiled in 100.0 water until completely decolorized. The hot liquid is filtered and a little zinc dust is added. To a small amount of the reagent are added an equal volume of extract from the studied stain and then several (3-5) drops of hydrogen peroxide. The presence of blood is detected by the appearance of a raspberry-red coloration of the upper part of the solution. This test is also obtained with some other substances (ferrous sulfate). 4) Schär's aloin test. To 10-20 drops of a 0.1% solution of Barbados aloin in a 70% aqueous chloral hydrate solution or 90% alcohol are added a few drops of 5% H₂O₂ and the extract from the suspicious stain. The presence of blood gives a cherry-red coloration to the solution. 5) Benzidine test (see). 6) Pyramidone test (Thevenon and Rolland). A 5% solution of pyramidone mixed with 50% acetic acid and 3% H₂O₂ gives a violet coloration with blood. 7) Fluorescein test (Fleig). Fleig's reagent (0.25 g of fluorescein mixed with 20 cm³ of KOH, 100 cm³ of water, and 10 g of zinc dust) is heated and filtered with the addition of 3% H₂O₂; in the presence of traces of blood, it gives strong fluorescence. 8) Alizarin blue test (Bajsch). Alizarinblau S, diluted to a yellow-red color, becomes blue upon the addition of hydrogen peroxide and blood. 9) Paraphenylenediamine test (Storch-Boas). A 0.5% aqueous solution of paraphenylenediamine hydrochloride with 3% hydrogen peroxide gives an olive-green coloration with blood, which then passes into brownish-red. 10) Leucomalachite green test (Firth and Michel). A 0.5% solution of leucomalachite green in acetic acid with 1% H₂O₂ in the presence of blood gives a green coloration. 11) Rhodamine test (Fuld). Reduced colorless rhodamine with 3% H₂O₂ gives a red coloration in the presence of blood. The cited tests and a number of others bear the name of "preliminary tests." A positive result of these tests is not absolute proof of the presence of blood, since it is also obtained with a number of other substances (pus, saliva, iron salts, potassium permanganate, etc.), which is why a number of authors recommend completely abandoning preliminary tests, while others believe that a negative result of these tests indicates the absence of blood, which is important in terms of simplifying the course of the study if there are many stains on clothing. Color reactions for blood are due to the fact that blood in them acts as a enzyme-catalyst, being an oxygen carrier. The sensitivity of all tests is very high (sometimes up to 1:1,000,000). In addition to color reactions for blood, reactions for blood protein (Beccadelli) and for iron (Riegler-Paleske) have also been proposed. The reactions are nonspecific, rarely used, and have not found wide application in forensic medical practice. Preliminary tests in no case preclude further studies for blood, which are carried out in the direction of detecting formed blood elements (erythrocytes) and blood pigment. Morphological tests. A small scraping is made from the object under study onto a glass slide. A few grains of the scraping are crushed and 1-2 drops of the reagent in which the study is performed are added to them. Then everything is covered with a coverslip and examined under a microscope after 20-30 minutes. Individual blood clumps swell and have a brownish-red color in the center and yellowish at the edges. In fresh objects, individual erythrocytes can be determined and even a micrometric study can be performed, while in older ones, individual erythrocytes are rarely encountered. Erythrocytes do not have their usual shape from drying and the action of the reagent, but appear uneven, angular, in the form of a mulberry. There are very many reagents.

The most common of these are: 1) a 33% KOH solution; 2) Marx's reagent (a 32% KOH solution mixed in equal parts with a 1:1,000 solution of quinine hydrochloride, with a few grains of eosin added); 3) Grigoriev's reagent (40 parts Rochelle salt, 12 parts caustic potash, 100 parts water). Older objects require more prolonged processing. Microcrystalline tests. 1) Crystals of hemin or hydrochloric acid hematin. A few grains are scraped from the surface of the stain onto a glass slide and crushed. One to two grains of table salt and 2 to 3 drops of glacial acetic acid are added to them. Everything is covered with a coverslip and heated carefully, without bringing to a boil. The presence of blood is proven by the appearance of brownish-yellow microcrystals in the form of rhombic tablets. If the crystals are poorly formed, they have the appearance of hemp seed. Obtaining hemin crystals definitively proves the presence of blood in the object under study. A negative result of the test is of no significance. The admixture of fat or rust makes it difficult to obtain hemin crystals. 2) Hemochromogen crystals, which can also be obtained from older objects from which hemin crystals cannot be obtained. To the scraping or aqueous extract from the stain, a few drops of Rieger's reagent (10 parts caustic potash, 50 parts 80% alcohol, 2 parts pyridine, 2 parts ammonium sulfide, 40 parts distilled water) are added, or a drop of the extract from the blood stain is mixed with a drop of pyridine, slightly warmed, and a drop of ammonium sulfide or hydrazine hydrate is added and covered with a coverslip. Under the microscope, the appearance of various forms of orange and bright red hemochromogen crystals is visible. In addition to the indicated reagents, various authors have proposed a number of others for obtaining hemochromogen crystals. 3) Strzyzowski's hydriodide-hematin crystals. Grains of the test substance are placed under a coverslip, at the edge of which are placed a few drops of the reagent (glacial acetic acid, distilled water, rectified alcohol 1 cm³ each, and 5 drops of hydroiodic acid), heated to boiling for 15-20 seconds with the constant addition of reagent. Crystals very similar to Teichmann's crystals are obtained. Microspectral tests. For microspectral research, derivatives of hemoglobin (hemochromogen and hematoporphyrin) are used. 1) Hemochromogen spheres. To a small amount of scraping from the stain, 3-4 drops of a 20-30% KOH solution are added on a glass slide and, covering with a coverslip, carefully heated 2-3 times until boiling begins. The red lumps turn into spherical figures (hemochromogen spheres) of various sizes of a brownish-pink color. Examination using a microspectroscope yields the characteristic absorption bands of hemochromogen (two in the green part of the spectrum - the left one sharp, dark, the right one pale). 2) A few drops of an aqueous extract from the blood stain are dried, and 2-3 drops of the reagent are added to the dry residue: 5 cm³ KOH, 10 cm³ distilled water, 10 cm³ pure glycerin, covered with a coverslip and slowly warmed; the mixture turns a bright red color. Microspectral analysis yields the spectrum of hemochromogen. In the case of stains from which hemochromogen cannot be obtained, hematoporphyrin is used to prove the presence of blood. 2-3 drops of concentrated sulfuric acid are added to the scraping from the stain on a glass slide and, covering with a glass slide, carefully warmed and microspectral analysis is performed. The presence of blood is proven by the characteristic spectrum of hematoporphyrin: one band, gray, in the orange part of the spectrum, to the left of D, and another, dark, between D and E in the yellow-green part of the spectrum. Examination in ultraviolet rays. Examination of objects in Wood's rays can also be attributed to preliminary tests, which makes it possible to search for washed-out blood stains that are invisible under normal lighting. In Wood's rays, washed-out blood stains appear dark brown. Thus, Wood's rays can be used to search for invisible traces of blood. The tests outlined above only prove the presence of blood without determining its species. To determine the species of blood in fresh objects, the following are used: 1) micrometric examination of erythrocytes, which have different sizes in different animals; 2) obtaining Hb crystals (determination of blood species by Hb crystals has not yet received recognition and dissemination due to the imperfection of research methods and insufficient study of this issue) and 3) the precipitation reaction (see Uhlenhuth reaction). Preliminary microcrystalline tests are also used in the study of seminal stains - Florence's, Barberio's, and Dominici's tests (see Barberio reaction, Dominici test, Florence test). Both a positive and a negative result of these tests does not provide grounds for concluding about the presence or absence of semen in the object under study. Only the presence of spermatozoa is definitive. Practically speaking, Florence's and Barberio's tests still have some value (orienting), making it possible from a multitude of stains present on soiled clothing (shirt) to subject only those stains with which the tests gave a positive result to subsequent microscopy for the detection of spermatozoa, which in a specific case can simplify the course of research. In Wood's rays, seminal stains cast a bright white color.