stained fabric may be moistened upon the slide and the fibers separated by picking apart with needles.

If the stain or clot be tolerably recent the corpuscles may begin to show themselves in a few minutes. With older stains the process may require several hours, or even days. Stains which are more than a week old act, under the operation of the solvent, in substantially the same manner as stains which are much older, and there is practically no difference, in most cases, between stains of a month's age and those of a year's standing, provided the specimens have been kept under conditions which have not affected the structure of the corpuscles.

In specimens under examination the portions of fluid immediately surrounding each particle become gradually tinted of a reddish or orange-yellow color from the solution of the blood-coloring matter, and when the decolorization is nearly complete the corpuscles begin to be visible. Very few perfect ones may be found, because most of them have become broken or distorted while drying. If, however, the drying has taken place under favorable conditions, if the stain has not been washed, subjected to heat or prolonged dampness, we may by searching almost always discover a few well-preserved corpuscles. If, under the treatment we have given, the characteristic disks make their appearance, there can be no question as to the character of the stain, but the observer must be certain that the cell-like structures which develop really are corpuscles. Serious mistakes have many times occurred where objects have been discovered which, under preconceived notions of the observer, have been pronounced corpuscles of blood.

The following remarkable case is within the personal knowledge of the writer:

In the case of Commonwealth vs. Piper, tried in Boston in 1875, the defendant, a sexton, was charged with the murder of a child in the belfry of his church. Certain articles having upon them suspicious stains were placed in the hands of several local experts for examination. Among the specimens was about a half-pint of water found in a pitcher in the basement, in which it was thought that the prisoner had washed his bloody hands. A short time previous to the trial, the experts, four in number, made their report of the results of their examination to the prosecuting officers, and every one of the four stated that the water contained blood-corpuscles which measured on the average about 1-3300 of an inch in diameter. This evidence was not given at the trial, because the government decided not to introduce any testimony in relation to blood, but the results stated in the report would undoubtedly have been given if it had been called for. A portion of the water was critically examined by Professor Wormley, and the bodies which had been confidently measured as corpuscles were proved to be merely the spores of a confervoid alga.

In the case of State of Connecticut vs. Hayden, tried at New Haven a few years since, a stone was produced at the preliminary trial which had been found in a field near the spot where a young woman had been murdered, and it was the theory of the prosecution that it had been used for striking a blow upon the head of the victim. The stone was stained with what appeared to be blood, and it was testified by a medical witness of some local celebrity that a microscopical examination demonstrated its presence. Subsequently, in preparation for the regular trial, the stone

was examined by another expert, and it was shown, and acknowledged by the first witness, that a mistake had occurred, and that spores had been taken for corpuscles.

The following case is given by Erdmann. (Zeitschrift fur Analyt. Chemie, vol. ii., 1862.) An assassination had been committed in Leipzig, and there was found near the spot where the crime had been perpetrated a brownish stain, which, under the influence of rain, assumed the appearance of coagulated blood. An aqueous solution of this stain furnished a reddish fluid, which gave with tannin, potassium ferrocyanide, and other reagents the same reactions as a solution of dried blood. Examined under the microscope, the brown matter was found to contain corpuscles similar to those of blood. The stain, however, failed to give any hæmin crystals when this test was applied, and this caused Erdmann to entertain doubts as to the value of the other tests. He repeated the microscopical examination with greater care, and then discovered that the bodies supposed to be blood-corpuscles were the spores of an alga, probably porphyridium cruentum, a vegetation so named on account of its resemblance to blood.

The disks found in pine, spruce, cedar, and other coniferous woods, the excrements of the cimex, spheroidal crystals of ammonium urate, oilglobules, air-bubbles, etc., are mentioned by writers as possible causes of error in suspected stains, but no microscopist of experience can possibly mistake any of them for blood-disks. The only dangerous fallacies are to be found in bacteria and spores. Bacteria are very much smaller than blood-corpuscles. The micrococcus known as prodigiosus, which in masses appears to the naked eye like fresh blood, has not one tenth the diameter of a blood-disk. But there are spores of various fungi and algae which in many instances have the same diameter as blood-corpuscles. The spores of porphyridium mentioned in Erdmann's case measure from 1-2900 to 1-3700 of an inch in diameter. (Rabenhorst.) Some of

Fig. 16.

the fluids which have been recommended by certain writers for soaking out the corpuscles from blood-clots, particularly sodium sulphate, sodium phosphate, and glycerin solution, if too much diluted will, in a few days, if kept in a warm place, develop spores some of which closely resemble decolorized bloodcorpuscles.

Richardson, referring to a preparation recommended by several writers, a saturated solution of sodium sulphate, says: "It must, I think, owe its popularity chiefly to the fact that it contains large quantities of fungus, the spores of which resemble blood-corpuscles both in size and general appearance, and have, I have no doubt, frequently been mistaken for blood-cells." (Amer. Jour. Med. Sciences, vol. lxviii., p. 109.)

Under the action of water, blood-corpuscles become globular and finally transparent and invisible, but spores are not in any way changed in appearance under the same circumstances. Spores are never disk-shaped, though they often

appear so. They are frequently oval and often circular; they may have buds upon them, and they are generally found in groups of two, three, or more. Close examination will, in many cases, show an interior structure wholly different from a blood-corpuscle. That they are a dangerous source of fallacy is proved by the instances we have given, and the observer should make it

a rule to first microscopically examine

the preparation with which he intends to soak up a suspected stain, and use only fresh or recently made solutions.

Materials found Associated with Blood. -Incidentally to the microscopic examination of suspected stains in the search for blood-corpuscles, other bodies may be discovered, of which careful note should be made. These may be one or more of the fol

lowing: fibers of silk,

wool, cotton, or linen; Fig. 17. a, Cotton Fiber; b, Air Bubbles; c, Portions of Feather; fragments of mineral

substances, as sand,

d, Silk; e, Oil Globules. (After Hofmann; 300 diameters.)

earth, bits of metal, etc.; hairs of various kinds, barbules of feathers, vegetable tissues, grass, wood, etc.; particles of bone, muscular fiber, cerebral matter, epithelium, etc. All such substances should be carefully preserved. They may furnish important evidence as to locality or circumstances. The limits of this article do not permit the discussion of the means of identification of these bodies, and the reader is referred to any good work on the microscope, as the treatises of Carpenter, Frey, Beale, and others.

MEASUREMENT OF BLOOD-CORPUSCLES.

If blood-corpuscles are found by the microscopic examination, it will be necessary to measure them. There are several methods by which this may be accomplished:

(1) By the screw micrometer.

(2) By photography.

(3) By the eye-piece micrometer.

The last is the most common as well as the most convenient method, and is the only one which we shall describe. The eye-piece micrometer in its simplest form consists of a circular glass plate ruled with fine lines (Fig. 17, B), which is cemented upon the diaphragm of the eyepiece between the field-glass and the ocular lens. The best arrangement

is that of a thin brass slide holding the ruled glass, which is inserted through a slit in the side of the eye-piece and has at one end a screw by which the micrometer can be given a slight lateral motion. The object to be measured is observed through the glass micrometer; one side of the object to be measured is brought exactly up to one of the lines, and the number of spaces which the object covers is carefully counted.

The value of the spaces of the eye-piece micrometer is merely relative, and dependent upon different objectives and varying adjustments of the instrument The value of the spaces is determined by a stage micrometer. This consists of a piece of ruled glass with spaces of 1-1000 of an inch. These spaces, when magnified and seen through the eye-piece micrometer, are covered by a certain number of lines in the latter. With a given objective, a 1-1000 space, for example, may be magnified until it covers five lines in the eye-piece; one of the latter spaces, therefore, measures 1-5000 of an inch. In most cases the eyepiece micrometer will not cover any certain number of full spaces, but there will be so many spaces and a fractional part of another space.

In such cases the draw-tube of the instrument must be extended until the increased amplification makes the space of the stage micrometer

B

Fig. 18. Eye-piece
Micrometer.

equal to a number of full spaces in the eye-piece. For convenience of calculation the number of these should, if possible, be some multiple of five or ten. If, under a high power (2500 diameters), forty spaces in the eye-piece are required to cover one space (1-1000 inch) of the stage micrometer, one space of the former will indicate 1-40,000 of an inch. Fig. 18, A, represents a portion of an eye-piece micrometer under a micrometry of 40,000, and the concentric circles the outlines of blood-corpuscles of man, the dog, rabbit, ox, and sheep. The largest corpuscle covers 12 spaces; its measurement is therefore 12.33-40,000 of an inch. Reducing this fraction to its simplest form, we obtain 1-3244. In the same manner we find that the corpuscle of the sheep covers 7 spaces, and therefore measures 7.75-40,000, which equals 1-5161.

We cannot enter further into the minute details of micrometry, but must not omit a single most important suggestion. No perfect stage micrometer was ever produced, and the observer must carefully compare and calculate the true value of each space which forms the basis of his measurements. An otherwise valuable piece of testimony may be completely shattered by a single question on cross-examination: "If you have not verified your micrometer, how do you know that your measure

ments are correct?"

THE DISTINCTION BETWEEN HUMAN AND OTHER BLOOD.

It is only by the microscope that any satisfactory distinction can be made between human and other blood. Various methods have been suggested depending upon other principles, but they have been found to be unreliable or impracticable in their application to dried stains. Barruel's process depends upon the production of an odor characteristic

of the particular animal when fresh blood is mixed with sulphuric acid. (Annales de Hygiene, 1829.) Taddei proposed to distinguish human blood from that of animals by the degree of fluidity produced in a compound of blood and carbonate of copper when treated with sulphuric acid. (For an account of Taddei's process, called hæmatolloscopy, and also Barruel's method, see Fleming's article on blood-stains in Am. Jour. Med. Sciences, vol. xxxv., p. 98, 1859.) Neumann claims that blood evaporated at a temperature of 60° F. gives a residue exhibiting certain appearances called "blood pictures," which are characteristic of different animals. (Die Erkennung des Blutes, Leipzig, 1869.)

There are two marked points of difference, under microscopic examination, between mammalian and oviparous blood: 1. The circular outline of the corpuscles of the former, in contradistinction to the oval shape of the latter; 2. The presence of a nucleus in oviparous, and its absence in mammalian, blood. Whether the stain be fresh or dry, recent or very old, these differences are apparent and unmistakable. Many instances have occurred in murder trials in which the defendant has claimed that stains on his clothing were produced by the killing of a fowl or were due to the blood of fishes. In all such cases, the falsehood, if it be one, is easily proved.

The possibility of distinction between the blood of man and the other mammalia has been claimed by several eminent authorities, including Schmidt, Richardson, Formad, Wormley, and Reese, and strenuously denied by others, especially by Woodward and Ewell. Nearly all writers on medical jurisprudence express grave doubts as to the value of opinions based upon variable fractional differences obtained by comparative measurements of corpuscles derived from dried stains.

The blood-corpuscles of most of the mammalia are smaller than those of man, so that when human blood is compared with that of the ox, for example, each being in a fresh state, by examining the specimens side by side upon the same slide (for an account of Richardson's method of preparing such slides, see American Naturalist, May, 1876) a difference in the diameters of the two is, even to the most careless observer, clear and unmistakable.

The diameters of the corpuscles of a large number of animals have been measured and their averages recorded. Suppose now that a specimen of mammalian blood of unknown origin and in a dried state upon cloth is subjected to microscopic examination: within what limits is the observer warranted in expressing his opinion as to its origin?

In answer to this inquiry, we remark that there is no fixed or invariable average for the diameters of the blood-corpuscles of any animal. It is true that the average does not vary beyond certain limits, but these limits have been shown by the observations of Woodward and Ewell upon the corpuscles of man and the dog to be much greater than formerly supposed. Not only is this true, but the averages given by differ ent observers, while agreeing closely in some instances, show considerable differences in others, so that, assuming the principle involved in this method of comparison to be correct, "it entirely depends," as Formad observes, "upon whose figures we accept whether we can or cannot discriminate between human blood and the blood of certain other animals."

The following tables give the average measurements of the bloodcorpuscles of man, dog, guinea-pig, rabbit, rat, mouse, opossum, wolf,