IDENTIFICATION OF HUMAN BLOOD AND HUMAN HAIR

In its structure blood may be described as a colourless fluid, the plasma having in suspension small solid substances—the red and white corpuscles. The plasma may be separated into a coagulated body termed fibrin and a transparent liquid called the serum. When blood coagulates, or forms clots, it forms a solid mass in which the red corpuscles are bound up in the fibrous mass of fibrin. The process of coagulation is promoted by moderate heat, slight dilution with water, and exposure to the air, while it is retarded by cold, strongly heating, great dilution and the addition of various chemical agents.

The red corpuscles differ in size and shape according to the species of animal. Thus in human blood and in the blood of most mammalia they appear as double concave circular discs, while in the blood of the camel and in that of birds, reptiles and fish the red corpuscles are elliptical in form.

The number of corpuscles present is also subject to great variations, the blood of amphibia and reptiles, for instance, containing remarkably few. The following numbers in 100 parts of the blood of different animals have been recorded: Horse, 53; pig, 43·5; ox, 35; dog, 35·7; and man, 48 corpuscles.

The colour of blood is due to a compound known as hÆmoglobin, which constitutes about 40 per cent. of the substance of the corpuscles. In the bright red arterial blood the hÆmoglobin is present in the form of oxyhÆmoglobin, and the latter may be separated in crystalline form by suitable treatment of the separated red blood corpuscles. These crystals differ in the case of different animals both in their chemical and physical characteristics, and have very different forms.

There are also similarly pronounced differences between the microscopical appearance of oxyhÆmoglobin crystals from human blood and from that of various animals. The crystals from human blood are in the form of long rhombic needles; those from the blood of the horse are quadrilateral prisms; the blood of the guinea-pig, rat, and many birds yield rhombic tetrahedea; while that of the squirrel gives hexagonal plates.

Crystals of other compounds of hÆmoglobin, such as hÆmin, differing in the case of different species of animals may also be prepared, and the identity of oxyhÆmoglobin may also be proved by its characteristic appearance in the spectroscope.

It is, therefore, under favourable conditions, not a very difficult matter to distinguish between the fresh blood of, say, a man and a squirrel by means of these characteristic differences. It is rarely, however, that the problem is presented in such a simple form in criminal work, in which usually all that is available for the investigation is the dried stain upon some garment or the clot upon a rusty knife.

One of the most widely employed tests is to dissolve a little of the material in acetic acid containing a little common salt, to apply a gentle heat to the microscope slide, and then to notice under the microscope whether hÆmin crystals are formed.

Where the stain is upon iron it is often impossible to prepare hÆmin crystals, and in such cases hydrogen peroxide is used as a reagent. This compound, when brought into contact with a fragment of the material moistened with alkaline water, gives off in the presence of blood, bubbles of oxygen, which gradually form a white scum.

Experiments made by M. Cotton have shown that the blood of different animals varies in the intensity of its action upon hydrogen peroxide. Thus human blood liberates about twice as much oxygen as the blood of the horse or pig, nearly four times as much as that of the ox and guinea-pig, and about ten times as much as the blood of the sheep.

Unfortunately other animal fluids have a similar action upon hydrogen peroxide, and the test can therefore only be regarded as corroborative evidence of the results obtained by other tests.

Attempts have sometimes been made by murderers to remove blood-stains by treatment with chemical agents, so as to prevent their identification.

For instance, in the trial of Misters for murder at Shrewsbury, in 1841, a solution of alum was found in his room, and it was supposed that he had removed the blood from his shirt by treatment with this. He was convicted, however, upon other evidence.

The identification of blood-stains upon rusty weapons is a more difficult matter than in the case of stains upon linen.

The action of the acid salts of fruits upon the iron may produce an appearance very similar to that of a blood-stain, the citrate of iron formed having a reddish colour which on more than one occasion has misled even a surgeon.

A case of this kind happened in 1838 in Paris. A man who had been accused of murdering his uncle, whose heir he was, was found to have a knife on the blade of which were stains, which everyone who saw them said were blood-stains.

A chemical examination, however, which was made in the presence of the magistrate and the prisoner, proved that they consisted of citrate of iron, and had been produced by cutting a lemon and neglecting to wipe the blade after use.

It has frequently happened in the past that the opinion of policemen or witnesses without any special knowledge of the subject has been taken in criminal cases on the point whether stains upon clothes or on a weapon consisted or did not consist of blood.

This practice was obviously a dangerous one, since even by the modern methods of examination it is not always a simple matter to be sure of the fact.

Until a comparatively recent date the tests for blood-stains were based upon bringing the colouring matter of the blood into solution and applying chemical tests to establish its identity.The necessity for scientific proof of the presence of blood-stains is shown by numerous cases in which stains of similar colour have at first been attributed to blood.

Thus in a case related in Taylor’s Forensic Medicine a man was arrested in 1840 on suspicion of being connected with a murder in Islington. He had in his possession a sack on which were numerous stains supposed to be dried and coagulated blood. When these were examined, however, they were found to be due to red paint.

In another case, a man who was suspected of a murder was found to have red stains on his shirt and collar, but as these would not dissolve in water they could not have been due to blood. Subsequently it was found that they had been caused by the man going out in the wet with a red handkerchief round his neck.

An early example of the way in which the evidence of an unskilled witness has been accepted upon the subject of blood is seen in the evidence given in 1682 at the trial of Thompson, Pain and Farwell for libel.

The libel arose out of the earlier trial in 1679 of Robert Green and others for the murder of Sir Edmund Godfrey, who had been waylaid and apparently strangled. This trial was one of those arising out of the so-called Popish Plot, and upon the evidence of Titus Oates, Miles Praunce and others the prisoners were convicted and executed.

Subsequently a letter to Mr. Praunce appeared in The Loyal Protestant Intelligence, which sought to make out that false evidence had been given at the murder trial, and that Sir Edmund Godfrey had not been strangled at all, but had committed suicide.

In the words of the prosecuting counsel for the prisoners—“they say that if a man or any other creature be strangled or hanged and the body cold and the blood settled in the veins (as he must be if your evidence be true, meaning the evidence of the said Miles Praunce). Run twenty swords through such a body not one drop of blood will come out; but, on the contrary, his body when found was full of blood. So that they do aver that that wound that he received by that sword must be the cause of death.”

William Batson, who was one of the principal witnesses for the prosecution, stated: “They showed me in a ditch where they said he lay some blood. I cannot say it was his blood; and going a little further I saw some more whitish blood, and this is all I can swear.”

The Lord Chief Justice (Scroggs) then asked if the weather had been frosty, to which the witness replied: “My lord, I cannot tell whether it was, but I will assure you the blood looked to me more like blood that was laid there than anything else.”

After a lengthy trial, in which the main evidence of the former trial, which was quite unconvincing, was repeated, the prisoners were found guilty of traducing the justice of the nation and two of them were sentenced to stand for an hour in the pillory and pay a fine of £100 each, while the third escaped with the fine only.

Where stains have been found upon the clothes or on a weapon in possession of an accused person and have been proved to consist of blood, the defence has frequently been set up that they were caused by the blood from a sheep that had been killed or from handling game.

Ten years ago, prior to the discovery of the serum test, it would not have been possible, except in the cases where the blood corpuscles could be examined, to prove or disprove this except by corroborative evidence. There was no chemical means of determining whether an old blood stain had been caused by the blood of a man or that of an animal.

Taylor, writing in 1844 upon this point, observes: “Some French medical jurists state that by mixing fresh blood with a certain portion of sulphuric acid and agitating the mixture with a glass rod a peculiar odour is evolved which differs in the blood of man and animals, and also in the blood of the two sexes. This odour, it is said, resembles that of the cutaneous exhalation of the animal, the blood of which is the subject of experiment. They have hereby pretended to determine whether any given specimen of blood had belonged to a man, a woman, a horse, sheep, or fish. Others pretend that they have been able to identify the blood of frogs and fleas!”

As Taylor pertinently observes of this: “There is probably not one individual among a thousand whose sense of smelling would be so acute as to allow him to state with undeniable certainty, from what kind of animal the unknown blood had really been taken. Any evidence short of this would not be received in an English court of law.”

On the first occasion upon which scientific evidence as to the difference between the blood of man and of animals was given in a criminal trial the remarks made by the judge (Lord Chief Justice Cockburn) to the jury showed that he was sceptical as to the powers claimed by the chemical witness of distinguishing between different kinds of blood.

In this case, which was tried at the Taunton Assizes, in 1857, a man had been found with his throat cut, and collateral evidence pointed to a man named Nation being the murderer. When he was arrested he was found to have a knife upon him on which were stains that appeared to be blood, but the prisoner accounted for these by saying that he had recently been cutting raw beef with the knife.

The chemical evidence, however, went to prove that coagulation of the blood had not occurred until after it had come into contact with the knife, or, in other words, that the blade had been plunged into living blood.

Moreover it was stated by this witness that the blood could not have been that of an ox, pig or sheep, since the corpuscles were smaller than those of human blood, whereas the corpuscles of the blood upon the knife were of the same dimensions as those of human blood. The relative sizes of human corpuscles compared with those of the animals mentioned were stated to be as fifty-three to thirty-four in the case of the ox; as fifty-two to thirty-four in sheep’s blood; and as forty-five to thirty-four in pig’s blood.

The judge, in his summing up, made the following comments upon the evidence: “The witness had said that the blood upon the knife could not be the blood of an animal as stated by the prisoner, and took upon himself to say it could not be the blood of a dead animal; that it was living blood and that it was human blood; and he had shown them the marvellous powers of the modern microscope. At the same time, admitting the great advantages of science, they were coming to great niceties indeed, when they speculated upon things almost beyond perception, and he would advise the jury not to convict on this scientific speculation alone.”

The jury found the prisoner guilty upon evidence other than this “scientific speculation,” the novelty of which probably prevented the judge from accepting it as a demonstration of facts which might be verified or disproved.

The application of a remarkable discovery in physiological chemistry has now made it possible to determine whether a blood-stain consists of the blood of any particular kind of animal.

In 1898 it was discovered by Bordet that on injecting serum of cow’s milk into a small animal, such as a rabbit, which was then killed after a lapse of some weeks, the serum separated from its blood would produce a precipitate in cow’s milk.

This discovery was supplemented by Wassermann, who, in 1900, found that it was possible in this way to distinguish between the milk of different kinds of animals, and he suggested the name precipitines for these specific precipitating agents formed in the sera of animals.

Then Dr. von Rigler showed that the method might be employed to distinguish between the flesh of different kinds of animals.

GOAT’S HAIR

COW’S HAIR

By kind permission of Messrs. Scott Greenwood & Co.

He prepared a 20 per cent. aqueous extract from the flesh of seven different species of animals, and injected small proportions of these beneath the skin of rabbits at intervals of three days. After a month the animals were killed, and the serum of the blood separated in a centrifugal machine.

In each case the specific sera were added to the clear filtered aqueous extracts of the flesh of the respective animals, and the tubes examined after the lapse of a specified time.

It was found that the sera only gave a turbidity or precipitate with the corresponding extracts. Thus the serum from the rabbit which had been treated with an extract of horseflesh only gave a reaction with preparations of horseflesh, and not with those of venison, beef, mutton or pork. In like manner, the serum from a rabbit that had been treated with an extract of rabbit’s flesh, only reacted with extracts of rabbit’s flesh, and not with those prepared from the flesh of cats, horses, or other animals, and so on.

In the case of mixtures the specific sera only reacted with extracts of the flesh of the two animals in question. Thus a rabbit treated with an extract from a mixture of the flesh of a hare, cow, deer, and pig, yielded a serum giving a precipitate with the extracts of the flesh of each of those animals, but not with that from any other animal.

It was not long before the possibility of using the method to distinguish between the blood of different kinds of animals suggested itself, and it was shown by Dr. de Nobel in 1902, that by treating a mouse or rabbit with any fluid, such as blood serum or saliva from a human body, it eventually produced a serum that would give a precipitate with human blood, but not with the blood of different species of animals.

Reactions were also obtained with old human blood. Thus stains on linen from several days to two months in age, when treated with dilute solutions of common salt gave a solution which yielded a precipitate with the prepared rabbit’s serum. No reaction was obtained, however, with the preparation from a blood-stain nine years old or with that from blood which had been dried in a high temperature.

It was also found that the specific sera could be evaporated in a vacuum without losing their activity, and that the dried residues could be preserved in sealed tubes in the dark, and mixed with water when required for use.

Other investigators showed that it was possible to separate the active agent by adding magnesium sulphate to the serum, and that the precipitate could be dried and kept for a long period. By dissolving it in water at any time a liquid with the specific properties of the original serum could then be obtained.

Later work has shown that this serum test is not quite so absolute as was at first believed. Thus, if the blood serum to be tested be used in too concentrated a form it may give a reaction with a serum that is not specific to it, though even in that case the precipitate will only appear slowly and its amount will be insignificant in comparison with that obtained when the two liquids correspond.

The error is obviated by using extremely dilute solutions for the test, and when proper precautions are taken a solution of normal blood serum containing one part in 1,000 invariably gives a reliable reaction with its corresponding prepared serum. In more concentrated solutions there is an abundant deposit at the bottom of the tube within thirty minutes, whereas in the case of sera, which are not specific to the prepared serum, the formation of precipitate does not begin until the tube has stood for an hour or more.

An interesting exception to the rule is that the serum from the blood of anthropoid apes gives a pronounced reaction with serum that has been made specific for human blood, and vice versa.

As it is not possible to carry out control tests with an indefinite number of animals a positive result obtained in the examination of a particular stain justifies a report that the blood was (e.g.) probably human blood and certainly not that of any common domestic animal.

On the other hand, the results of a negative test justify a much more positive statement.

Thus on the first occasion in which evidence was given as to the results of this test, which was in a criminal case in France in 1902, the prisoner had asserted that certain incriminating stains had been caused by the blood of a rabbit.

A serum specific for rabbit’s blood serum was therefore prepared, and the stains dissolved and tested as described above. No sign of precipitate was obtained within thirty minutes after applying the test and evidence was therefore given that the stain certainly did not consist of rabbits’ blood. On the other hand, a serum made specific for human blood gave an immediate precipitate with the solution of the stain, which, therefore, in all probability consisted of human blood.

Although this method of testing blood-stains has been used on the Continent for several years, it is only within the past twelve months that it has been employed in a criminal case in this country.

Apparently the first occasion was in the recent trial of Mark Wilde for the murder of Mr. George Storrs, a mill-owner, at Gorse Hall. Evidence was given that old stains were present upon the outside of the sleeve of the prisoner’s blue serge coat, although they were not visible to the naked eye. These were found to consist of mammalian blood, and the serum test for human blood gave a positive reaction. It was, of course, impossible to form any idea as to the age of the stains, and the witness, Dr. Wilcox, refused even to give an estimate upon this point.

A simple method of applying the serum test has recently been discovered. A small quantity of human serum is placed into a series of tubes, and into each of these is next introduced one drop of the fresh blood of different animals diluted with salt solution, or of the dried blood dissolved in that liquid.

The tubes are now allowed to stand for thirty to forty-five minutes and are then examined. If in the case of the blood of unknown origin there is a faint red precipitate (of coagulated blood) leaving the upper liquid quite clear, the blood is of human origin.

On the other hand, the blood of other species of animals will have dissolved in the human serum, colouring it red.

RABBIT’S HAIR

HORSE HAIR

By kind permission of Messrs. Scott Greenwood & Co.

If the tubes are charged in the first place with the blood of the horse, ox, or other animal, the corresponding blood is coagulated, while that of any other animal dissolves. In this way it is possible to apply the physiological test without the necessity of preparing a special serum by inoculation.

From time to time in criminal trials, the latest instance being in the Crippen case, the question occurs whether a given specimen of hair is of human origin or has been derived from an animal. Thanks to the pronounced difference in appearance shown by hairs of different origin when viewed under the microscope there is no difficulty in giving a positive answer to this question.

Human hair is characterised by being fairly uniform in diameter throughout most of its length and then tapering gradually to a fine point. The hair of an infant has very few scales upon its surface, and these stand out prominently, but in the case of an adult the scales are very numerous and appear closely pressed against the axis of the fibre. Another peculiar point of difference between the hair of a young child and that of a full-grown person is that in the case of the former there are some particulars in which the hair resembles that of certain animals. Thus it has a jointed appearance recalling to some extent the structure of the fibres of merino wool.

In the hair of many animals the medulla, or central canal, is plainly visible under the microscope, but such medullated fibres are apparently not formed in the case of human hair.As the hair of many domestic animals might on superficial examination be mistaken for human hair, it is essential to take note of the characteristic differences, some of which are shown in the accompanying figures.

Three types of hair are found upon the cow, viz.: thick beard hairs, showing a medulla, soft woolly hairs, and fine beard hairs, both of which are without a medulla. In those fibres in which it is present the medulla is very pronounced and tapers towards the apex. The hair of the calf has the same structure as that of the cow.

Horse-hair is characterised by its lustrous cylindrical appearance. The commercial fibre is mainly derived from the mane and tail, and is much thicker and stiffer than the hairs from the body, which are those most likely to be met with in criminal investigations. As a rule, the latter are less than an inch in length, and the medullary canal is well marked.

In rabbit’s hair the medulla is also very pronounced and is characterised by its structure of curious quadrilateral cells, which may either form a single row or increase to four or eight rows as the hair becomes wider. On the surface of the hair are numerous scales which fit into one another after the manner of the joints in a bamboo cane.

The chief commercial use of the rabbit’s hair, which is usually about half an inch in length, is the manufacture of linings for hats.

The hair of the cat has a superficial resemblance to that of the thinner hairs of the rabbit. The medullary canal is very prominent, and occupies more than half of the fibre. It is made up of a single series of quadrilateral cells, but unlike the cells in rabbit’s hair, these may form additional layers in the thicker parts of the hair. The hair is generally a little over half an inch in length, and tapers to a fine point.

WOOL FIBRES

From different breeds of Sheep

By kind permission of Messrs. Scott Greenwood & Co.

Dog’s hair differs from the hair of the cat both in size and appearance. It is about three times as wide, while the medullary canal only occupies about one quarter of the diameter of the fibre. The surface of the hair is covered with characteristic scales, the edges of which project, so that the edge of the fibre has a saw-like appearance.

The accompanying plate shows hair taken from a Pekin spaniel and Persian kitten, and drawn to the same scale of magnification (104 diameters).

In the hair of the kangaroo the serrated edge of the fibres, due to projecting scales, is much more pronounced than in dog’s hair. The medulla is well marked, but lacks the cellular structure to be seen in the hair of the cat and rabbit.

Goat’s hair could not possibly be mistaken for human hair under the microscope. It has a root of characteristic appearance, and shows a well-marked medulla containing a structure of narrow cells.

Towards the middle the hair becomes very narrow, but expands again and reaches its greatest diameter a little before the point.

Sheep’s wool is characterised by its surface structure of scales, the arrangement of which differs in the wool from different breeds of sheep. In some of the fibres the medullary canal is very manifest. Typical fibres of sheep’s wool are shown in the figures.It is often necessary to distinguish between fabrics of cotton, linen, silk and wool, and in such cases the microscopical appearance of the fibres is invaluable as a preliminary test. Cotton is characterised by its curious corkscrew-like twists, and linen by its jointed structure, while silk has a long smooth cylindrical fibre, devoid of scales and showing little sign of structural formation.

In criminal cases neither cotton nor silk are likely to be claimed as human hair, although one may easily conceive the possibility of occasions arising where the composition of a peculiar material was a point of the utmost importance.

COTTON FIBRES

FLAX FIBRES

By kind permission of Messrs. Scott Greenwood & Co.