Stains may require detection on clothing, on cutting instruments, on floors and furniture, etc. The following are the distinctive characters of blood-stains:

(a) =Ocular Inspection.=--Blood-stains on dark-coloured materials, which in daylight might be easily overlooked, may be readily detected by the use of artificial light, as that of a candle, brought near the cloth.

Blood-spots when recent are of a bright red colour if arterial, of a purple hue if venous, the latter becoming brighter on exposure to the air. After a few hours blood-stains a.s.sume a reddish-brown or chocolate tint, which they maintain for years. This change is due to the conversion of haemoglobin into methaemoglobin, and finally into haematin.

The change of colour in warm weather usually occurs in less than twenty-four hours. The colour is determined, not entirely by the age of the stain, but is influenced by the presence or absence of impurities in the air, such as the vapours of sulphurous, sulphuric, and hydrochloric acids. If recent, a jelly-like material may be seen by the aid of a magnifying-gla.s.s lying between the fibres. If old, a cinnabar-red streak is seen on drawing a needle across the stain.

(b) =Microscopic Demonstration.=--With the aid of the microscope, blood may be detected by the presence of the characteristic blood-corpuscles.

The human blood-corpuscle is a non-nucleated, biconcave disc, having a diameter of about 1/3500 of an inch. All mammalian red corpuscles have the same shape, except those of the camel, which are oval. The corpuscles of birds, fishes, reptiles, and amphibians, are oval and nucleated. The corpuscles of most mammals are smaller than those of man, but the size of a corpuscle is affected by various circ.u.mstances, such as drying or moisture, so that the medical witness is rarely justified in going farther than stating whether the stain is that of the blood of a mammal or not. Unfortunately, the corpuscles are usually so dried that little information regarding their size can be given.

(c) =Action of Water.=--Water has a solvent action on blood, fresh stains rapidly dissolving when the material on which they occur is placed in cold distilled water, forming a bright red solution. The haematin of old stains dissolves very slowly, so employ a weak solution of ammonia, and this will give a solution of alkaline haematin. Rust is not soluble in water.

(d) =Action of Heat.=--Blood-stains on knives may be removed by heating the metal, when the blood will peel off, at once distinguishing it from rust. Should the blood-stain on the metal be long exposed to the air, rust may be mixed with the blood, when the test will fail. The solution obtained in water is coagulated by heat, the colour entirely destroyed, and a flocculent muddy-brown precipitate formed.

(e) =Action of Caustic Potash.=--The solution of blood obtained in water is boiled, when a coagulum is formed soluble in hot caustic potash, the solution formed being greenish by transmitted and red by reflected light.

(f) =Action of Nitric Acid.=--Nitric acid added to a watery solution produces a whitish-grey precipitate.

(g) =Action of Guaiac.u.m.=--Tincture of guaiac.u.m produces in the watery solution a reddish-white precipitate of the resin, but on addition of an aqueous solution of peroxide of hydrogen, or of an ethereal solution of the same substance (known as _ozonic ether_), a blue or bluish-green colour is developed. This test is delicate, and succeeds best in dilute solutions. It is not absolutely indicative of the presence of blood, for tincture of guaiac.u.m is coloured blue by milk, saliva, and pus.

(h) =Haemin Crystals (Teichman's Crystals).=--These are produced by heating a drop of blood, or a watery solution of it, with a minute crystal of sodium chloride on a gla.s.s slide and evaporating to dryness.

A cover-gla.s.s is placed over this, and a drop of glacial acetic acid allowed to run in. It is again heated until bubbles appear. Crystals of haemin may now be detected by the microscope. They are dark brown or yellow rhombic prisms.

An improvement on this test is the use of formic acid alone; on slowly evaporating it, numerous very small dark crystals are visible if haemoglobin has been present (Whitney's test).

(i) =Spectroscopic Appearances.=--If a solution of a recent stain be examined by the spectroscope, we get two absorption bands situated between the lines D and E, the one nearer E being doubly as broad as the other. These bands indicate _oxyhaemoglobin_.

If we now add a little ammonium sulphide to this solution, we get the spectrum of _reduced haemoglobin_, which is a single broad absorption band situated in the interval between the preceding oxyhaemoglobin bands. By shaking the solution, oxyhaemoglobin is again reproduced, and gives its special absorption bands.

If ammonia be added to the original solution, _alkaline haematin_ is produced, or if acetic acid be chosen, _acid haematin_ is produced, and each gives its appropriate absorption bands.

_Methaemoglobin_ is formed in stains which have been exposed to the air for a few days, and _haematin_ is found in old stains. _Haemochromogen_ gives a very characteristic spectrum, and is obtained by reducing alkaline haematin by ammonium sulphide. _Carbon monoxide haemoglobin_ gives a spectrum which resembles that of oxyhaemoglobin, but it is not reduced by ammonium sulphide.

(j) =Precipitin Test.=--This allows us to tell whether the blood is from a human being or not. A specific serum must be obtained from a rabbit which is sensitized as follows: 10 c.c. of human blood is injected into its peritoneal cavity at intervals, until from three to five injections have been given. The serum of this animal's blood will then give a white precipitate only when brought into contact with dilute solutions of human blood, but with the blood of no other animal. This is known also as the 'biologic,' or Uhlenhuth's test.

=Rust Stains.=--These are yellowish-red in colour, and do not stiffen the cloth. The iron may be dissolved by placing the stain in a dilute solution of hydrochloric acid, when, on adding ferrocyanide of pota.s.sium, Prussian blue is produced.

=Fruit Stains= are seldom so dark as blood-stains. Solutions of these do not change colour or coagulate on boiling; ammonia changes the colour to blue or green; acid brightens the original colour, while chlorine bleaches it.

=Hairs.=--Human hairs must be identified and distinguished from those of the lower mammals. If the hair has been pulled out from the root, the microscope will show that the bulbous root has a concave surface which fitted over the hair papilla, or that the root is encased in a fatty sheath.

=Fibres of Clothing.=--Microscopically, wool fibres are coa.r.s.e, curly, and striated transversely; cotton fibres appear as flattened bands twisted into spirals; linen fibres are round, jointed at frequent intervals, with small root-like filaments; silk fibres are solid, continuous, and highly glistening.

XVI.--DEATH BY SUFFOCATION

_Signs and Symptoms._--There are usually three stages:

1. Exaggerated respiratory activity; air hunger; anxiety; congested appearance of face; ringing in ears.

2. Loss of consciousness; convulsions; relaxation of sphincters.

3. Respirations feeble and gasping, and soon cease; convulsions of stretching character; heart continues to beat for three to four minutes after breathing ceases.

_Post-Mortem Appearances--External._--Cadaveric lividity well marked; nose, lips, ears, finger-tips almost black in colour; appearance may be placid or, if asphyxia has been sudden, the tongue may be protruded and eyeb.a.l.l.s prominent, with much b.l.o.o.d.y mucus escaping from mouth and nose.

_Internal._--The blood is dark and remains fluid; great engorgement of venous system, right side of heart, great veins of thorax and abdomen, liver, spleen, etc. Lungs dark purple in colour; much b.l.o.o.d.y froth escapes on squeezing them; mucous lining of trachea and bronchi congested and bright red in colour; air-cells distended or ruptured; many small haemorrhages on surface of lungs and other organs, as well as in their substance (_Tardieu's spots_), due to rupture of venous capillaries from increased vascular pressure.

XVII.--DEATH BY HANGING

In hanging, death occurs by asphyxia, as in drowning. Sensibility is soon lost, and death takes place in four or five minutes. The eyes in some cases are brilliant and staring, tongue swollen and livid, blood or b.l.o.o.d.y froth is found about the mouth and nostrils, and the hands are clenched. In other cases the countenance is placid, with an almost entire absence of the signs just given. The mark on the neck, which may be more or less interrupted by the beard, shows the course of the cord, which in hanging is obliquely round the neck following the line of the jaw, but straight round in strangulation. In judicial hanging, death is not due to asphyxiation, but, owing to the long drop, the cervical vertebrae are dislocated, and the spinal cord injured so high up that almost instant death takes place. On dissection the muscles and ligaments of the windpipe may be found stretched, bruised, or torn, and the inner coats of the carotid arteries are sometimes found divided. In ordinary suicidal hanging there may be entire absence of injury to the soft parts about the neck, the length of the drop modifying these appearances. The mark of the cord is not a sign of hanging, is a purely cadaveric phenomenon, and may be produced some hours after death.

XVIII.--DEATH BY STRANGULATION

This differs from hanging in that the body is not suspended. It may be effected by a ligature round the neck, or by direct pressure on the windpipe with the hand, in which case death is said to be caused by _throttling_. Strangulation is frequently suicidal, but may be accidental. When homicidal, much injury is done to the neck, owing to the force with which the ligature is drawn. In throttling, the marks of the finger-nails are found on the neck.

XIX.--DEATH BY DROWNING

Death by drowning occurs when breathing is arrested by watery or semi-fluid substances--blood, urine, etc. The fluid acts mechanically by entering the air-cells of the lung and preventing the due oxidation of the blood. The post-mortem appearances include those usually present in death by asphyxia, together with the following, peculiar to death by drowning: Excoriations of the fingers, with sand or mud under the nails; fragments of plants grasped in the hand; water in the stomach (this is a vital act, and shows that the person fell into the water alive); fine froth at the mouth and nostrils; cutis anserina; retraction of p.e.n.i.s and s.c.r.o.t.u.m. On post-mortem examination, the lungs are found to be increased in size ('ballooned'); on section, froth, water mud, sand, in air-tubes.

The presence of this fine (often blood-stained) froth is the most characteristic sign of drowning. Froth like that of soap-suds in the trachea is an indication of a vital act, and must not be mistaken for the tenacious mucus of bronchitis. The presence of vomited matters in the trachea and bronchi is a valuable sign of drowning. The blood collects in the venous system, and is dark and fluid. Tardieu's spots are not so frequently met with in cases of drowning as in other forms of asphyxia. The other signs of death by asphyxia are present. Wounds may be present on the body, due to falling on stakes, injuries from pa.s.sing vessels, etc.

The methods of performing artificial respiration in the case of the apparently drowned are the following (the best and most easily performed is Schafer's p.r.o.ne pressure method):

1. _Schafer's._--Place the patient on his face, with a folded coat under the lower part of the chest. Unfasten the collar and neckband. Go to work at once. Kneel over him athwart or on one side facing his head.

Place your hands flat over the lower part of his back, and make pressure on his ribs on both sides, and throw the weight of your body on to them so as to squeeze out the air from his chest. Get back into position at once, but leave your hands as they were. Do this every five seconds, and get someone to time you with a watch. Keep this going for half an hour, and when you are tired get someone to relieve you.

Other people may apply hot flannels to the limbs and hot water to the feet. Hypodermic injections of 1/50 grain of atropine, suprarenal or pituitary extracts, may be found useful.

2. _Silvester's._--In this method the capacity of the chest is increased by raising the arms above the head, holding them by the elbows, and thus dragging upon and elevating the ribs, the chest being emptied by lowering the arms against the sides of the chest and exerting lateral pressure on the thorax. The patient is in the supine position--but first the water must have been drained from the mouth and nose by keeping the body in the p.r.o.ne position. The tongue must be kept forward by transfixing with a pin.

3. _Marshall Hall's._--This consists in placing the patient in the p.r.o.ne position, with a folded coat under the chest, and rolling the body alternately into the lateral and p.r.o.ne positions.

4. _Howard's._--This consists in emptying the thorax by forcibly compressing the lower part of the chest; on relaxing the pressure the chest again fills with air. Here the patient is placed in the supine position.

The objections to the supine position are that the tongue falls back, and not only blocks the entrance of air, but prevents the escape of water, mucus, and froth from the air-pa.s.sages.