Blood Stains. Various medico-legal questions are often to be solved concerning the nature of stains resembling those made by blood. The principal of these are: 1. Is it possible, and by what means, to decide that a stain is produced by blood or not? 2. Is it possible, and by what means, to ascertain that the blood of a stain comes from a man or from an animal? 3. Is it possible to find out whether the blood of a stain comes from one man or another? I. It is usually easy to ascertain whether a stain is due to blood or not, either by the chemical test of reagents or the physical test of the microscope. The latter is the more decisive, but a complete medico-legal examination must comprise both of them. If there is a stain of suspected blood on a piece of cloth, or any other stuff, the stained part must be cut off and dipped into a small quantity of distilled water. In the course of a few hours the coloring matter, if it is that of blood, will detach itself and reach the bottom of the vessel, the supernatant fluid remaining tolerably clear or slightly rose-colored. The fibrine will remain attached to the stuff as a grayish or rosy-white substance.

If the liquid be boiled, the color will be destroyed and the albumen coagulated; in its inferior parts, where the coloring matter has accumulated, the liquid will become grayish or greenish, while the upper portion will acquire a slightly yellow tint. The red soluble dyes, or stains from the juices of fruits, are very rarely coagulated, and they do not lose their color when, after having been dissolved in water, the solution is boiled. Besides, they are rendered crimson or green, passing sometimes to violet, when treated with ammonia, while this reagent, unless it be used in great quantities and concentrated, does not change the color of blood or of a watery solution of a blood stain. "When ammonia is powerful enough to alter the color of blood, it gives it a brownish tint, instead of the crimson, green, or violet colors that it gives to dyes. If the solution of a blood stain has coagulated by boiling, we find that potash dissolves the coagulum, rendering it limpid and green by reflection, and pink by refraction. If chlorhydric acid is then added, the transparency disappears, but it returns if another quantity of potash is added. These reactions belong only to blood.

The nature of the smallest stain, able only to furnish one drop of a solution, may be found out by the above-mentioned chemical means. In such circumstances, according to Boutigny, the drop should be thrown into a silver spoon at a very high temperature. The liquid in this, as in any other case, i. e., with any kind of liquid whatever, being suddenly exposed to an extreme heat, instead of evaporating takes the shape of a sphere, and then experiments may easily be tried, and the action of ammonia, of potash, of chlorhydric acid, etc, may rapidly be ascertained. - The microscope usually shows more quickly and positively than chemical reagents whether a stain is due to blood. With the help of this instrument the red and the colorless corpuscles may be seen easily. (See Blood.) There is nothing to be found with the microscope in the stains of the various dyes which can in any way be mistaken for the blood corpuscles. The presence of these well characterized particles in a stain is therefore an incontestable proof that it contains blood. But the blood corpuscles may have become so much altered that it is very difficult to ascertain their presence, at least without the help of chemical reagents. The microscope, unaided by chemistry, therefore, may fail to detect blood in old stains.

However, it is usually easy to find the red corpuscles, and they have been detected in stains of many years' duration. Dr. Taylor says that he has obtained clear evidence of their existence in a small quantity of blood, which had been kept in a dry state for three years. Dr. Charles Robin has discovered the presence of red corpuscles on clothes in stains of eight or ten years' duration. Prof. Jeffries Wyman says that in blood which had been allowed to dry in masses he has failed to find the red corpuscles, while, on the contrary, the white or colorless corpuscles may be softened out after they have been dried for months, and their characteristic marks readily obtained. He found it easy to detect them in blood which had been dried for six months. Dr. Robin has given a drawing representing what the microscope showed in a solution of a stain found on the blade of a knife. No red corpuscle is figured, while on the contrary many colorless ones are. But the mere fact of the presence of colorless corpuscles, with nearly the same appearance that they have in fresh blood, is not sufficient to prove that a stain is due to blood, because the chyle and lymph corpuscles, those of pus, and even some of those of mucus, are similar to the white corpuscles of the blood.

When clothes have been washed after having been stained with blood, nearly or quite all the corpuscles are removed, or so much altered that their presence cannot be ascertained positively. But chemistry may then render it very probable that there has been blood on such clothes, by detecting in them iron and a coagulable organic matter. If blood stains are on the blade of a knife, the microscope and chemical reagents may enable us to distinguish them from rust. Usually, when the knife is heated, a blood stain may be peeled off, leaving a neat metallic surface where it was; it is not so with rust, which remains almost unaltered. Besides, when the stain is washed, it leaves a much smoother surface if it is due to blood than if it comes from rust. Usually in this latter case there is a peculiarly dentated surface, the presence of which leaves no possibility of a mistake. In a case where Daubrawa was requested to ascertain the existence of blood stains on a knife which was suspected to have been used in the commission of a murder, this instrument, having lain a long time in a damp place, was rusted, but there were certain bright spots free from rust, and surrounded by it.

On heating the point of the blade these spots scaled off, while the rust remained adherent; and on immersing the knife in diluted hydrochloric acid, the bright spots remained unaltered while the rust readily dissolved. Some of the reagents which serve to detect blood were then employed, and it was found that the bright spots wore really covered with blood, which had prevented the formation of rust. In another case in which a man had been accused of murder, an examination of a knife covered with fed spots, and found concealed behind a piece of furniture, proved that the stains were due to rust produced by lemon juice. Blood may be detected even on a stone. Prof. Lassaigne ascertained its presence a full month after it had been shed on a pavement of soft freestone, which had been exposed to the action of air, of rain, and of the sun. The color of the stain had passed to a dirty green, with a reddish tint hardly discernible. In a place where stains of blood are suspected to exist, and where none are found by daylight, the search for the red spots must be made by artificial light. In a case where Ollivier d'Angers had vainly tried by daylight to find stains of blood on the floor and on the paper hangings of a room, he detected many by candlelight.

II. When it is decided that a red stain is due to blood, it remains to be ascertained if the blood is that of a man or of an animal. Chemistry in such an examination is of little avail. The physical character of the red corpuscles of the blood is almost the only guide. It has been said, however, that some reagents may develop in the blood such a smell that it is easy to determine not only from what animal the blood comes, but also whether it is that of a man or of a woman. When sulphuric acid is added to the blood of an animal or of a man, it gives rise to a smell which has been said to be just the same as that of the individual that furnished the blood. The chemist (Barruel) who discovered this fact was almost always able to make out by this means what was the source of blood sent to him; so were Colombat and some other physicians; but decisive examinations have shown that very few have the organ of smell sensitive enough for this purpose. In man and all the mammalia (except the camel tribe), the red corpuscles are circular, flat disks, while in most fishes, in reptiles, birds, and camels, they are oval. In a case mentioned by Taylor, it was suggested in the defence that the blood stains on the clothes of the prisoner were due to his having killed some chickens.

The shape of the globules negatived this part of the defence. In another case the blood was alleged to be that of a fish; this was also disproved by the shape of the corpuscles. Dr. H. Bennett of Edinburgh states that a patient having bronchitis had put bird's blood in her sputa, and that after the microscope had shown this fact she was greatly surprised that it had been discovered, and confessed that she had done it for the purpose of imposition. On looking at the table of the dimensions of the blood corpuscles (see Blood), it will be found that the blood disks of man are larger than those of all the domestic animals. To cover the extent of a linear inch requires 3,200 of the red corpuscles of a man, 4,404 of those of a cat, and 6,366 of those of a goat. C. Schmidt thinks he has shown that by accurate measurements of the red corpuscles, the blood of all the common mammalia can be individually detected and also distinguished from that of man. He proposes to avoid the errors arising from a greater or a slighter evaporation, by drying the blood corpuscles before measuring them.

He gives the following table:

Diameter Of Blood Corpuscles In Millimetres

Dr. Taylor says he has tried the method of Schmidt and has not found it practically available, and he declares that the question of the distinction between the blood of man and that of certain animals is unsolved. He adds that when blood has been dried on clothing, we cannot with certainty and accuracy distinguish that of an ordinary domestic animal from that of man. Usually, however, in fresh blood, the measurement of the red corpuscles will decide the question; and in old stains, when the blood corpuscles have changed their form and become jagged or stellate, it will often occur that several substances will give them their normal shape and render possible the determination of their source. But the evidence here is based on conjecture only, and should therefore be received with the greatest caution. Not only can the red corpuscles be altered in their size and shape, but they may be decomposed and give origin to crystals which are so similar, whether coming from the blood of certain animals or that of man, that no distinction is possible. Fortunately there are almost always at least a few undecomposed red corpuscles among the crystals. III. It is absolutely impossible to distinguish the blood of one man from that of another by means of the comparison of the red corpuscles.

There may be more difference between the corpuscles of two samples of blood from the same man than between those of two men. A great many external causes may produce variations in the size of the red globules; and besides, the proportion of water and of certain gases or salts in the blood has a great influence on the shape and dimensions of the red corpuscles. All who know the facts advanced in favor of or against the theory of Henle, concerning the causes of the difference of color of the arterial and venous blood (see Respiration), are aware of the changes of the blood corpuscles due to oxygen, carbonic acid, etc. The smell of the blood of women might by some persons be distinguished from that of the blood of men, but we cannot place any reliance on the senses of anybody for such a distinction; and we know that even Barruel, who discovered the influence of sulphuric acid in increasing the odor of blood, once failed to distinguish the blood of a man from that of a woman. Chemistry also is of no avail for the discrimination of the blood of one man from that of another.