The Medical Detective and His Work by T. F. Manning


wing to the fact that they often flatly contradict one another, medical experts do not stand very high in popular repute; nevertheless, it is a positive fact that a single medical expert is worth half Scotland Yard in the detection and prevention of crime. Thousands of rivals in love, disagreeable husbands, dangerous political agitators, harsh masters and mistresses, rich uncles, and people of that sort, would be popped off with a few grains of arsenic, or a drop of prussic acid, only that it is well known the doctor has the eyes of a hawk for poison. And, on the other hand, many and many a family is saved from the suspicion attaching to the sudden death of a member, and even many an innocent man from the scaffold, by the proof of natural death which the doctor supplies.

Although great poisoning, shooting, stabbing, and other homicidal trials have a wonderful fascination for all newspaper readers, very few fully appreciate the medical evidence, which is usually the most important link in the chain. The evidence is of three kinds—that of the ordinary medical man, who sees the patient dying, perhaps, and performs the post-mortem; that of the chemist, who, in his quiet laboratory, traces the poison or identifies the blood stain; and that of the expert, who gives his inference from the facts stated by the first two. It is these experts who often differ from one another.

In a large number of cases the post-mortem examination is the first step in unravelling a mystery.

The man who performs it is not to be envied, for the smallest scratch on his hand may admit a dose of deadly poison.


Many medical men, indeed, wear rubber gloves, and those less careful generally cover their hands with a layer of sticky ointment. It takes from two to four hours to do the job thoroughly.

But it is not all cutting up, as most people think. The first thing done is to notice the position of the body, and whether there are any weapons, bottles, or glasses near.

Then it is examined from head to toe for scratches, cuts, bruises, moles, tattoo marks. Everything about the hair, eyes, teeth, nose, ears, and other parts, is written down. The height, the age, the muscular development, are all noted.

Of course, this inspection alone often reveals the cause of death. Suppose, however, that no external injury is found and no organ is diseased, the suspicion of poisoning naturally arises. In that case, the doctor looks for certain marks that the commonest poisons make, and then he places the stomach and other parts in glass jars, which are securely covered, sealed, labelled, and handed to the analyst.

Poisoning is not much favoured by the Briton as a means of killing either himself or anybody else. He generally does the deed in a more open, if more brutal, way. But it is to be feared that a great many more people get rid of undesirable contemporaries in this manner than is popularly supposed.


Probably, in most cases, the ordinary medical attendant is able to tell whether a person is dying a natural death or is being carried off by some deadly drug. His position, however, is not a pleasant one. It is impossible to be certain; and, in order to make a full investigation, he must suggest either that the victim is committing suicide, or that someone else, perhaps his wife or son, is committing murder. And, after all, the signs in the living are very obscure. Of course, if a person is foolish enough (as many are) to drink sulphuric or nitric acid, his mouth and throat are burned as if he swallowed coals of fire, the former leaving black and the latter yellow stains; but when the poison is arsenic, or opium, or strychnine, the symptoms are very like those of certain diseases.

When the cholera was last in London, a father, mother, son, and daughter dined together. Immediately after dinner, all, except the son, became suddenly ill, and died in a few hours, with the symptoms of arsenic poisoning.

The son, who was always quarrelling with the rest of the family, was arrested on the doctor's report and charged with murder. But a post-mortem examination showed that cholera was the real cause of death.

Apoplexy, in the same way, is very like opium poisoning; and hydrophobia, lock-jaw, and even some cases of hysteria, closely resemble poisoning by strychnine.

Still, when a healthy man grows suddenly ill soon after a meal, the doctor keeps his eyes open, and if death follows he has a pretty shrewd idea of what caused it.

At all events, he feels perfectly justified in assuming that the case is not a normal one. He therefore hands over to the analyst the jars and other receptacles containing the portions of the subject's body likely to bear traces of the poison, knowing full well that if any poison is there the analyst will infallibly detect it.

The analyst begins by making a series of what may be called "brews," mincing, pounding, boiling, cooling, filtering, decanting, and distilling, over and over again. In these operations various solvents are used in succession, plain water separating out one class of poisons, alcohol dissolving out another group, benzol taking up a third, naphtha a fourth, ammonia a fifth, and so on. This preliminary work takes, not hours, but days to perform. At an early stage in it the operator discovers such volatile poisons as prussic acid, chloroform, carbolic acid, and phosphorus, if any of them be present. Later on he comes across the alkaloids, such as strychnine, digitalin, cantharidin, and other terrible poisons of that class.

Finally, the residue of the animal matter with which we have supposed the medical detective to be experimenting is mixed with hydrochloric acid, and distilled once again, after which it can contain no poison except one of the metals.

Thus, in the course of his examination, the analyst has made a number of decoctions, in one of which the poison is certain to be. In each decoction there may be any one of several groups of poisons.

In which is it, and what is it? After all this patient labour the solution is still far off. It may be a ptomaine from poisonous fish or decayed meat, a deadly berry, or leaf, or root, a small quantity of morphia, or phosphorus, or lead, or arsenic, or antimony.

Each brew is tested in turn. But, as illustrating the general procedure, take the last, which contains whatever metal may have had the fatal result. First, the chemist tests with "group reagents." He knows that if he puts into the glass containing the last brew certain bodies in succession, some metals, if they are there, cannot be kept from rushing into the arms of one, others will as passionately embrace another, others still will unite with a third, while some will always repudiate any alliance. There are in all cases signs of the union, when it takes place, such as a blue or white or red colour, or a powder falling to the bottom, or a fizzing of escaping gas.

In practice the analyst puts a little of the brew in a small glass test-tube, pours in some distilled water, and carefully drops in some hydrochloric acid. Now, if there is either silver, mercury, or lead, in the brew, down goes a white powder; if none of these things is there, no change follows.

Next he adds some sulphuretted hydrogen water, a sort of aerated water smelling of rotten eggs. If tin, platinum, bismuth, cadmium, arsenic, or one of several other metals, is in the brew, a coloured powder falls to the bottom. Should nothing occur, he adds other things, until he has tested for five groups of metals.

When he finds a poison belonging to a certain group, he has still to ascertain which of five or six bodies it is.

For instance, after adding the first two test-liquors, if he sees a yellow coloration or precipitate, he knows that he has either arsenic or tin or cadmium. He then adds some strong ammonia, after boiling the liquid till the smell of rotten eggs has disappeared. If the powder dissolves, and the colour goes, he is quite sure he has found arsenic.

In this business-like way the murderer is convicted.

But now arises the necessity for making doubly sure, and another kind of test altogether is employed. Life and death hanging on the result, the test must be beyond all doubt. But arsenic is one of those self-assertive things about whose presence there cannot be the most infinitesimal doubt. Give a man a particle the size of a mustard-seed, and let him swallow it. When he dies bury him, and let him lie under the earth for a quarter of a century. Then gather the few remnants, give them to a chemist, and he will return you a considerable portion of the poison in the same state as that in which it was administered.


Probably the most famous special test for arsenic is Marsh's, the invention of a Woolwich chemist, and equally famous is Reinsch's, which is performed as follows: The suspected liquid is put in a little glass test-tube with some hydrochloric acid. Then a small bit of bright copper is dropped in, and the test-tube is held over a flame.

Now, arsenic has the wildest love for copper, and every trace of it in the tube flies to the slip of copper and covers it with a grey coat. Another metal does the same, certainly, but they can be distinguished subsequently.

Presently the copper is removed, washed, dried, and placed in a tough glass tube, very narrow at one end. This is held over a flame and carefully heated, and then a phenomenon, not unknown, either, in the loves of mortals, occurs. The arsenic abandons the copper, and clings in crystals to the sides of the glass tube, where it can be recognised by the aid of a magnifying-glass or microscope; and if the crystals are heated with a bit of acetate of potash the odour drives the chemist from the room.

To this curious fact, that arsenic loves copper when it is wet with warm hydrochloric acid, and hates it when it is hot and dry, is due the discovery of many a crime.

It is already plain to the reader that the analyst's task is not an easy one. Sometimes the analytical examination is of vast extent; sometimes it is greatly narrowed by hints from the family doctor. These hints are interesting, and show that the doctor is, when he knows his business, a real and a very skilful detective.

The doctor's eye is a wonderful one. When he enters a room, he not only measures the patient from head to toe, notes the colour of his face, the posture of his body, the signs of pain, stupor, or perhaps sham; but observes the manner of the other people present, and sees every bottle, glass, and cup in the place.

Now, although sudden death is usually from natural causes, when it occurs soon after food there is always suspicion, as we have said. So, if the doctor perceives great pain and nausea, he thinks of arsenic, antimony, tinned meats, mushrooms, toadstools, and other things; if the pupil of the eye is as small as a pin-head, and the sick man is drowsy, he thinks of opium; if something seems to have caught hold of the patient's heart, and to be squeezing it like a sponge, he thinks of digitalis; if the poor victim is being worked like a puppet, and his pupils are large with fear, he thinks of strychnine; if there is great thirst, colic, and cramps in the legs, he thinks of lead.


He knows that prussic acid kills like a bullet in the brain—a glass of cold water taken while hot from exercise may do the same—and he smells for it. He can also tell if it is phosphorus or carbolic acid, by the smell.

He knows that relatives usually kill each other by means of particular poisons; that other poisons are used for suicidal purposes; that the photographer takes cyanide of potassium, the medical man and chemist prussic acid or morphia, the poor man vermin-killer or oxalic acid, or carbolic acid, or some such agonising destroyer of life. And thus, though all poisons lead to the same end—stoppage of the breathing and blood circulation—yet each has its own particular way of sending the soul to eternity. He can therefore often tell the analyst detective how to take a short cut.


By the way, there is no such thing as a slow poison—that is, a poison which, taken to-day, does not show its effects for weeks. This is a fiction of the novelists. On the other hand, there is—except in the case of prussic acid and nicotine—no death straight away after taking poison, as one sees it on the stage, Shakespeare notwithstanding.

An actual case will show that the discovery of murder by the doctor and analyst is not always plain sailing.

A good many years ago, a Mr. Sprague was tried for the murder of the Walker family by means of the well-known poison of the deadly nightshade. The medical evidence showed clearly that they all died from belladonna poisoning, and belladonna was found in the rabbit-pie they had for dinner. A common-sense jury, however, acquitted the prisoner; and only recently have medical men solved the mystery by discovering that rabbits can eat any quantity of this plant without suffering harm, while their flesh becomes fatally poisonous.

A second case shows what wonders the chemists can work. A surgeon's wife died from corrosive sublimate, given in a draught by her husband. He said that, in making up the draught, he mistook a bottle of mixture, which he had prepared for a sailor, for the water-bottle, and had poured some of it into his wife's draught. The sailor's mixture was analysed, and it certainly contained corrosive sublimate; but, not content with finding the poison, the analyst measured the quantity present, and, while the sailor's mixture contained only ten grains to an ounce of liquid, the wife's draught contained fifteen grains, showing that the surgeon's ingenious explanation was a lie!

Blood is so characteristic a fluid that it might be supposed a skilful analyst could never have any difficulty in recognising it. Of course, if he were given, say, a cupful in its ordinary state, he could not make a mistake. But he never gets a chance of earning his fee so easily.

When the police seek his assistance they give him, perhaps, a suit of dirty clothes, which may be stained by two or three small dark spots that might be anything.

Or perhaps he is given a rusty knife, or a perfectly clean hatchet, and is asked to say if there is blood on it. And when he comes into court he is expected to tell the jury whether the blood is human or animal, how old it is, was it spilled from a living blood vessel, and in what part of the body was this blood vessel.

Take an actual case. Years ago a celebrated murder was committed in Eltham, and in the report of Dr. Letheby, the analyst, is the following note:—

"On the evening of May 3rd I received from Mr. Mulvaney" (of the police) "a brown paper parcel containing a pair of dark trousers, a man's shirt, and a man's wide-awake hat. On the following evening I received from Mr. Mulvaney a brown paper parcel containing a lock of hair, a pair of men's boots, and a plasterer's hammer."

These were all very dirty, but that did not prevent the analyst from finding a number of blood stains and hairs, and giving valuable and decisive evidence at the trial.


What the analyst first does, when he receives such an article as a pair of trousers, is to scrutinise every inch of its surface with a magnifying glass. If he finds a little lump of dark-coloured stuff he scrapes it off and puts it into a watch glass. If he discovers merely a dark stain, he cuts out the piece of cloth and puts it into a small quantity of distilled water.

Now he has to find out whether the suspicious-looking thing is really blood, or whether it is merely red paint, or logwood, or cochineal, or madder, or iron-mould. There are three ways of doing this, and he nearly always utilises them all.

First, there is the marvellous spectroscope test. This test will reveal the presence of the minutest trace of blood, and it is practically infallible. It depends on the curious property, possessed by nearly all bodies, of absorbing certain parts of the light that passes through them. Sunlight passing through a prism is split up into the familiar seven colours of the rainbow. But if a little blood dissolved in water is placed in a glass tube, and if the light is made to pass through it on its way to the prism, the blood takes something out of it; for now among the seven bright colours are seen two dark bands near the middle of the yellow ray. Nothing but blood gives these two bands in that particular place, with the exception of two or three substances that are not likely to be found on criminals' clothes. These are cochineal, mixed with certain chemicals, hot purpurin sulphuric acid, and the red dye of the banana-eater.

Blood, however, changes after it is shed. In stains a few weeks old the colouring matter changes from what is technically called hæmoglobin to methæmoglobin, and, later still, to hæmatin. All of these give different spectra. The analyst has standard spectra already mounted, and he invariably looks at the mounted or standard specimen and the suspected liquid at the same time, placing them side by side, so that a mistake is impossible. All the red colours in the world, in fact, have been tried, and, with the exceptions named above, none of them gives a spectrum like the colouring matter of blood in any of its forms.

But though the spectroscope is a certain discoverer of blood, it can draw no distinction between human and animal blood. That duty remains to the microscope.

Man. Mouse. Horse. Camel.
Toad. Pike. Pheasant. Pigeon.

With the microscope can be seen those red corpuscles which, in some mysterious manner, seize on the oxygen of the air as it passes into the lungs, shoulder it, so to speak, and rush away with it, like so many ants, to the remotest parts of the body. Unfortunately, they can only be seen in blood that has not been very long shed—that is to say, some weeks or months. To see these, the analyst scrapes the little clot from the piece of cloth, or wood, or iron, and places it on a slip of glass; over this he carefully lays the little film called a cover-glass; and then he gently places, at the edge of the latter, the tiniest possible drop of water. This gradually insinuates itself, and soon dissolves the blood clot; and, when the mixture is placed under a microscope magnifying from 300 to 500 diameters, he sees one of several pictures. The various shapes and arrangements taken by these little bodies are illustrated on the following page. Small as they are—it would take 12¼ millions to cover a square inch—they have the most peculiar way of behaving, and only the practised eye of the microscopist can recognise them in all their disguises.


Individually, the blood corpuscle is just like a tiny round biscuit, and measures 1/3200 to 1/4000 of an inch across its face. It is these two factors, the shape and measurement, which enable the medical man to say whether the blood is human. The picture above shows how a corpuscle looks under the microscope. Looking at its face, it is like a thick-edged biscuit, with a dark depression in the centre. Some are turned sideways in our illustration. These exist in blood and nothing but blood, so that, when the spectroscope fails, the microscope succeeds.

But it is not always that the analyst can get sufficient blood to place under the microscope. Perhaps he gets a piece of cloth saturated with a trifle of red fluid which he cannot scrape off, or perhaps he gets a stain some months or years old (Dr. Tidy identified a blood stain one hundred and one years old), in which the corpuscles are destroyed. Or perhaps he gets a garment which has been carefully washed, on which there is only the faintest trace of colouring matter. Even then the microscope tells whether the stain is blood.

Our detective mixes the particle of blood-stained wood, or earth, or dust, or cloth fibres, with water and caustic potash, and filters it. Then he takes a drop of the liquid and places it in the useful watch-glass. Into this he puts some glacial acetic acid and a crystal of ordinary table salt. He heats the mixture and lets it cool. And, if it is blood, he gets peculiar crystals visible under the microscope. These, by the way, differ to some extent in different animals.

Another test is so new that it has not yet been given a fair trial. It is as follows:—If a fairly large quantity of blood can be got, it is burned, and the ash is analysed. Now, there are two salts always in blood—sodium and potassium salts. But, while the quantity of the former in human blood is usually twice that of the latter, it is six times as great in the sheep's blood, eight times as great in the cow's blood, and sixteen times as great in the blood of a fowl. Very important results are expected from this principle.

Reliable as are the microscope and spectroscope, the analyst always uses the third means at his disposal—the chemical test. For instance, he gets a knife covered with dark red stains. Are they blood, or are they only the rust formed by vinegar or the juice of a lemon that has deceived so many people? Assuming that he has removed the stain, he places the matter in any kind of tiny vessel, and drops in some tincture of galls. If the thing is only rust, he has some excellent blue ink; if it is blood, he finds that a reddish powder makes its appearance.


Perhaps he gets a handkerchief with a red stain. If the cloth is white he can apply a test direct to it, but as a rule he prefers to dissolve the stain out. Now, a handkerchief may be stained with a number of different reddish things—Condy's fluid, jam, cochineal log-wood, or red paint. He puts a drop of ordinary ammonia on the cloth. If the stain is caused by currant, gooseberry, or other fruit juice it turns blue or green; if it is Condy's fluid it becomes blue; if it is cochineal it becomes crimson, and so on. But if it is blood, it does not change in the least. Other tests might be described, but we have not the space.

Probably the most interesting of all his duties to the analyst is that of judging from what animal the blood stains came. This can be done only in some cases; that is, when the blood is not quite so old that the red corpuscles have entirely lost their shape.

Of course this is a matter of the greatest importance when a man is on his trial; for, in the first place, every spot of blood found on his belongings is supposed to have come from his victim, although it may be nothing more than the blood of a fish; and, in the second place, the stock explanation of blood stains on his clothing offered by a prisoner is that they came from some animal he killed. The plan is to ask him what animal. Five times out of six he will say a domestic fowl or some kind of bird especially if he is a poacher who has killed a gamekeeper—and then he is done for.

Look at the pictures on page 149 and you have the whole thing in a nutshell. It will be seen that the red corpuscles of the blood of birds, reptiles, and fishes (with the exception of the cyclostomata) are oval, while those of mammalian blood are round. Here is, at once, a sure way of differentiating mammalian blood from that of the other three great classes of animals. The only difficulty is that blood corpuscles get out of shape, under certain circumstances, and are no longer either oval or round. But there is another difference. A mammalian corpuscle is of uniform substance throughout: that of a fish, bird, or reptile has a small, dense spot near the centre, called a nucleus. Snails, slugs, worms, and other low forms of animal life do not come into the question at all, for their blood is generally colourless, and, if not, it is blue-green, violet, brown, being scarcely ever red, and then not from the presence of corpuscles.

All that remains for the analyst, therefore, supposing he finds a round corpuscle, is to say to what mammalian animal it belongs. (The llama, alpaca, camel, and their kin, by the way, have oval corpuscles.)

How are the corpuscles of different mammalia to be distinguished under the microscope? Merely by their size. They have all been measured with the greatest care, a specially small unit of length, called a micron, having been invented for the purpose. It is only 1/25000 of an inch long, and, expressed in tenths of a micron, the average diameter of a human blood corpuscle is 77; of a dog, 73; of a rabbit, 69; of a cat, 65; of a sheep, 50; of a goat, 41; and of an elephant, 94. But these are average measurements, and some corpuscles are smaller, some larger.

Cat's HairBat's HairBerlin Wool.Reindeer's Hair.Woody Fibre.
Human HairFox HairHare's HairSquirrel's Hair.Human Hair Bulb.

Therefore, when it is a question of whether the blood is that of a dog, pig, hare, rabbit, or man, he would be a daring man that would give a decided opinion. But it is certainly possible to come to a safe conclusion as to whether it is that of a human being or a sheep, goat, or elephant.

Owing to the influence of disease on the blood, however, it is never really safe to say absolutely "This is human blood," and, in fact, all that is generally stated in evidence is whether it is mammalian.

There is one other important piece of work the medical detective can perform in his laboratory, in the way of tracking criminals; that is to distinguish hairs from vegetable fibres, and human hairs from animals'. Our illustrations show how it is done. He simply places the thing to be tested under the microscope, and—as he is acquainted with every description of hair, cotton, wool, silk and other fibre—he can tell at a glance what it is.

Hair is more like wool than anything else, but wool is irregular and hair is pretty regular in breadth. The hair of an adult, also, has a streak in the middle.


We append accurate illustrations, from microscopic photographs, of the hairs of many animals. Obviously, there is no difficulty to the practised eye in distinguishing them. In fact, most animals' hairs can be known by the naked eye, or with a small magnifying glass; but that of skye terriers and spaniels is wonderfully like human hair.

On all these little things hinges, very often, the terrible issue of "guilty" or "not guilty"!

Some years ago, a woman was found dead with a knife lying loosely in her hand. This fact might mislead people into thinking it was a case of suicide; but the fact that the knife was not held tight made the doctor suspicious. He examined the blood on the knife, and found woollen fibres which resembled those of the husband's clothes. This discovery so acted on the husband that he confessed his guilt.

On another occasion a Taunton man was seen last in company with a man subsequently found dead. In the Taunton man's possession was a knife with a slight film of blood on the blade. He said he had been cutting raw beef. The analyst easily showed, however, that the blood on the knife came from a living animal; and, further, he found on it some little scales from the lining of the human gullet. The Taunton man was convicted.

A remarkable instance of the analyst's power was given in a Cornwall murder case. A man was found with his head broken. On a hammer belonging to a suspect were a couple of grey hairs. This hammer, however, had been used for beating goat-skins, and, in fact, it was found in a hedge on which a goat-skin was spread out to dry.

But the medical witness swore that the two hairs came from somebody's eyebrow, and, on comparing them with the dead man's eyebrow, they corresponded!

In one case a man was very near being hanged—and in the old days, doubtless, he would have been hanged—mainly because a knife with red stains was found in his possession. The medical witness found that they were rust caused by an acid fruit; and then it was found that the prisoner had actually used a knife for cutting a lemon. But, curiously, this stain is so very like blood that the naked eye of even the most skilful medical jurist would be deceived by it.



Footprints are usually left to the police to interpret. But, very probably, the result is often a miscarriage of justice. When the police are working up a case they would not be human if they did not view evidence with a certain amount of bias. The scientific witness, on the other hand, has no personal interest one way or the other. And, moreover, the comparison of a naked foot with its supposed print on the ground, or the fitting of a boot to a boot-mark, is a process requiring not only the most exact measurements, but consideration of the kind of mark made on different kinds of soil, and in the various positions taken by the foot in standing, walking, and running. In running we press mainly on the toes, and in walking the greater part of the foot comes down, and the longer the foot rests on the ground the deeper is the impress. In fact, an expert can make a pretty shrewd guess as to the rate at which the owner of the foot was travelling, by considering the size and depth of the footprint.

In order to make a comparison a cast has to be taken, if the mark is on soft ground. This is done by heating the footprint with a hot iron, and filling it in with paraffin. From this a plaster cast is taken, and it can be preserved for comparison until someone is arrested.

When the footprint is found in snow, gelatine is used to take the form of it, and from this also a plaster cast is made.

Of course, these operations have to be carried out with the greatest care, for footprints are frequently the strongest pillars of an indictment. In order to compare the foot of the suspected person, he is made to walk, stand, and run, over a surface similar to that on which the incriminating print has been found. There is one case in which the scientific detective is certain—when the person has stood still on soft, but firm and tenacious, soil.

The footprints represented in our sketch are those of course of naked feet, which give the clearest impression. But a corresponding variation occurs in all footprints made by persons wearing boots, so that the attitude or action of the wearer is easily told.

Now and again some deformity, such as the possession of six or of only four toes, leaves no room for doubt. When the mark has been made by boots, rather than with the naked foot, it is frequently easy to identify it by the arrangement and number of the nails, by a missing nail, or a patch, or a hole, or a heel worn on one side.

Nevertheless, footprints are, to the medical man, exceedingly doubtful evidence, although from this view the police, and probably the jury, differ.

Taking him altogether, the medical detective does his work with a skill, certainty, and absence of prejudice, worthy of emulation by all engaged in hunting down the criminal. The story of modern medical detective work is one of the most romantic of our times.