WHEN LIFE OR DEATH HANGS ON A BLOOD STAIN. HOW SCIENCE SOMETIMES SERVES THE ENDS OF JUSTICE. By William Franklin Watson, Expert in Microscopy, Furman University, Greenville, U.S.A.

Progress, Volume II, Issue 2, 1 December 1906, Page 66

WHEN LIFE OR DEATH HANGS ON A BLOOD STAIN. HOW SCIENCE SOMETIMES SERVES THE ENDS OF JUSTICE. By William Franklin Watson, Expert in Microscopy, Furman University, Greenville, U.S.A.

In cases of murder, stains supposed to be blood are sometimes found on the clothing or belongings of suspected persons. In doubtful cases of this kind, the fate of the defendant usually depends, not so much on judge, jury, or eloquent lawyers, as on the observations of a man who, quietly seated in his laboratory, is compelling with his microscope the invisible to become visible. When the prisoner claims that certain dark red stains on his clothing were caused by spatters of red pamt, the judge and jury and the lawyers cannot prove or deny the statement. They may say : "It looks like blood." But what do value resemblances amount to, since, in so many of the affairs of life " things are not what they seem ? " A human life hangs in the balance. It must neither be sacrificed by vague suspicions, nor saved if the suspect is guilty. The man with a microscope and a laboratory is the only person who can settle the question, and he can settle it beyond the shadow of a doubt. He dissolves a particle of the stain m a drop of liquid, then spreads a minute fraction of this drop on a little slip of glass three inches long and an inch wide. Next he examines it with the microscope. If he sees a great host of little red discs, such as appear highly magnified, he knows that the stain was made by blood. But suppose the stain is old and has been exposed to the weather for weeks or months. It has become greatly changed. It can be dissolved only with difficulty ; and the little blood discs, if present, may be shrivelled, distorted, and broken up, until it is impossible to determine whether they are real blood discs or particles of something else. When the blood has reached this state, it is impossible to use any chemical which will restore the discs to their original condition. Consequently, it is frequently impossible to identify old blood by means of its discs. In such cases the investigator takes a particle of the stain on a glass slip, and dissolves it in strong acetic acid, adds a minute portion of common salt, and heats it with extreme care. Great skill is here required in order to heat just sufficiently and not too much. The glass slip is then examined with the microscope ; and if a great number of stick-like, X-shaped (and occasionally stellate) crystals appear, the stain is known to be blood. These are called " Teichmann's crystals " (from the discoverer). They are regarded by experts as yielding evidence which is absolutely conclusive. They can be produced by no known substance except blood. Another important method for the detection of blood is that of spectrum analysis, which depends on its optical characters and requires more complicated apparatus than the other processes. The fourth test which may be applied to blood is strictly chemical. A small portion of the suspected substance is put on clean, white paper, and is moistened with tincture of guaiacum. A drop of hydrogen peroxide is next added, when, if the substance tested is blood, the paper will turn to a beautiful blue colour. A particle of blood which is scarcely visible to the naked eye may be detected in this way. The human blood discs are very small. It would take 3,200 of them placed side by side in. a row, to measure one inch in length Though very minute, they are so numerous that a volume of blood not larger than the head of a pm is believed to contain five millions of them. In fact, they are present in the blood in such vast numbers that some scientists have made the astonishing statement that if all the blood discs which are in one person were arranged side by side in a continuous line, that line would be long enough to reach four times around the earth Without discussing the differences between blood from the veins and that from the arteries, and the differences in colour as affected by the different substances on which it falls and dries it may be noted that in general, when blood stains are fresh, their colour is scarlet and they dissolve readily in water. As the stains get older they become darker, first changing to reddish brown and later to dark brown. They also become less and less soluble in water Finally they become entirely insoluble in water, and chemicals must be

used for their solution. From these facts it will be seen that the analyst can, under favourable conditions, determine the age of blood stains. He cannot be exact m his conclusions, it is true, but he can say whether the stain is a few days old, a few weeks old, or a year old. By the examination of a blood-spattered surface, one does not need to be a Sherlock Holmes to determine pretty accurately the direction of fall of the drops and the distance from which they came. An important question arises After determining that the stain is blood, can the investigator decide whether it is human blood or the blood of a beast ' In deciding this question, he must rely entirely on the microscope. All chemical tests give exactly the same results, whether the blood is that of a man, a bird, or a reptile. Many suggestions for differentiation along this line have been made, which, however, would not stand the test of practical experiment in the laboratory , many fine theories have been advanced, only to be overthrown. So it must be acknowledged that up to the present time it has been found impossible by any other process or instrument to distinguish human blood stains from those of other animals. But under favourable conditions, when the blood is fresh, the microscope will give results which are satisfactory and reliable. The blood discs of birds and reptiles are oval and nucleated, while human blood discs are circular and have no nucleus. The blood of pigeons and frogs may be taken as types of blood of birds and reptiles. Therefore, if a man who is arrested for murder claims that certain stains on his clothing were caused by killing a chicken, a reptile, or a fish, the microscopist can easily determine the truth or falsity of the statement. The camel and llama have oval blood discs like those of birds and reptiles ; but all other higher animals classed as mammals have circular blooddiscs closely resembling those of human blood. In fact, the resemblance is so close that the only way of determining the difference is by measuring the discs. For this purpose, exceedingly delicate instruments are used in connection with the microscope. The blood of sheep, goats, horses, and cattle has discs which are considerably smaller than those of human blood. But monkeys, dogs, rabbits, and guinea pigs have blood discs so nearly like those of man that it appears doubtful if it is possible for any scientist to decide positively between them. It has also been found impossible to distinguish the blood of a man from that of a woman or child, or the blood of any one person from that of another under any ordinary circumstances. Notwithstanding the limitations mentioned, the specialist has m very many cases, rendered eminent service in the identification and conviction of criminals.