We are not aware that this knowledge has thus far been of the slighest use in medico-legal investigation, but it may become so, as the histological studies of blood by this author are of the greatest value. I shall conclude this short paper with a few replies received from scientists to whom I wrote for their views upon the question of whether there was any means, now known to science, to enable the observer, by the microscope or in any other manner, to distinguish between the blood of man and the domestic animals, and notably those mammalia whose red corpuscles approximate nearest to those found in human blood. Prof. Marshall Ewell, President of the American Microscopical Society, replied as follows: CANTON, O., May 4, 1892. My Dear Sir:-I had occasion, as an expert in the celebrated case of the murder of Dr. Cronin, to examine the question proposed for discussion, and came to the conclusion, which I have since seen no reason for modifying, that it is impossible by any means at present known to science to discriminate between dried human blood and that of the dog, rabbit, guinea-pig, or of any other domestic animal. My reasons for this opinion are given at length in a paper entitled "A Micrometric Study of 4,000 Red Blood Corpuscles in Health and Disease," a copy of which I have contributed to the MedicoLegal Society, and which is published in No. 2, Vol. 10, Medico Legal Journal. My experience in the subject of microscopy, in which I have specialized for the last eight years, leads me to the conclusion that there is not only no advantage in the use of very high powers (1-25 or 1-50), but a positive disadvantage, if the power is so high as to impair the definition, as appears to have been the case in the work recorded in the monograph of Dr. Formad, judging from his published engravings. Dr. Formad, of Philadelphia, in that paper, appears to me to have misquoted authorities to such an extent as to lead me to repose no confidence whatever in his published results. I know of no new advance in science in relation to the identification of blood stains since the publication of my paper above referred to. Respectfully yours, M. D. EWELL. Dr. Robert Reyburn, of Washington, D. C., Vice-President American Microscopical Society, was present and took part in the discussion of the paper. He said: The question of the method of distinguishing between the blood corpuscles of man and the ordinary domestic animals is one of great forensic importance, and has also been one of the most vexed questions in microscopical science. The human red blood corpuscle, or cell, as is well known, is a circular disc, which is bi-concave, or hollowed inwards, on both its surfaces. When seen singly they are of a yellow hue, though in quantity, as seen in the arterial blood, they are of a scarlet red color. We have also existing in blood the white corpuscles, which are slightly larger than the red, being 10 to 12 microns, or 1-2750 to 1-3000 of an inch in diameter, and also the blood plates, or tablets of Bizzozero, which are from 2 to 3 microns, or 1-8000 of an inch in diameter, one-third the size of the red corpuscles; however as these component parts of the blood do not offer any satisfactory means of identification in blood stains, or clots, it will not be necessary to dwell farther upon them. The human red blood corpuscle varies for 7.9 microns, or 1-3200 of an inch, to 6.9 microns, 1-3500 of an inch, in diameter, and are about onefourth that in thickness (or 1 9.10.) The variation in size of the corpuscles will rarely vary more than from 10 to 12 per cent. of the number of any blood corpuscles in any specimen of human blood. Examined we will find from 80 to 90 per cent. of the number of human corpuscles present of the average size, viz: 1-3200 to 1-3500 of an inch. Dr. Formad, in his Monograph (Comparative Studies of Mammalian Blood), gives the following coparative measurements of blood corpuscles : Man, 1-3200 of an inch; guinea pig, 1-3400 of an inch; wolf, 1-3450 of an inch; dog, 1-3580 of an inch; rabbit, 1-3662 of an inch; ox, 1-4200 of an inch; pig, 1-4250 of an inch; horse, 1 4310 of an inch; sheep, 1-5000 of an inch; goat, 1-6100 of an inch. After giving these various dimensions of the blood corpuscles of different animals, the question naturally arises: Where is the difficulty in measuring these? Can we not, by the accurate micrometers and microscopes we now possess, measure them just as accurately as the carpenter measures any square surface by the use of a rule or tape measure? This, however, is not the real difficulty. Our instruments of precision are amply capable of meeting the exigencies of the case, but the difficulty lies in an entirely different direction. The trouble in our investigation of this subject lies in the fact that the blood corpuscles are living organisms that are not possessed of outlines delineated with mathematical accuracy. They vary in the same animal, and in different species of the same animal, to such a degree as to greatly impair the accuracy of the deductions to be drawn from even the most accurate series of measurements. Dr. J. G. Richardson, in papers published in American Journal of Medical Sciences, July, 1869, page 50, and July, 1874, page 102, states, as the result of his investigation, that he could invariably distinguish between the dried blood corpuscles of the man and the sheep when so situated that he could not know from what source they were derived. He states (page 106 A. J. M. Sciences, July, 1874, or the 16th May, 1874,) my friends, Prof. J. J. Reese and D. S. Weir Mitchell, prepared for me these three packages of dried blood, from stains made by sprinkling the fresh fluid (blood) from an ox, a man, and a sheep on white paper. These stained pieces of paper were numbered 1, 2, and 3, respectively, and given to Dr. Richardson to examine, and he succeeded perfectly in distinguishing the source from which they came by the use of the microscope. Dr. J. J. Woodward (A. J. M. Sc. Jan., 1875, p. 151,) controverts the arguments of Dr. J. G. Richardson, and states that he believes it to be impossible to distinguish between the blood corpuscles of man and several of the domestic animals; though he confines his argument more especially to the similarity in size of the blood corpuscles of the dog to those of man. He states (p. 158) that on making each measurement of blood containing 50 corpuscles from as many men their sizes ranged from 7.72 microns to 7.54 microns. He compared these measurements with nine specimens of blood of different species of dogs, measuring 50 corpuscles each time, and found their sizes to range from 7.42 microns to 7.37 microns. These measurements are so nearly alike that they seem to be practically identical, and the known accuracy and skill of Dr. Woodward gives his opinion great weight. He further says, (p. 156, ) “For myself, after repeated measurements of the blood of the dog and human blood, I can only say that I find no constant difference between them, whether the fresh blood or thin layers dried on glass be selected for measurement." The mean of 50 corpuscles taken at hazard is seldom twice the same, and sometimes that of human blood, sometimes that of dog's blood, is a trifle the largest. In his Monograph, Comparative Studies of Mammalian Blood (p. 19 and 47), Dr. Henry F. Formad has shown, however, that the measurements given by Dr. Woodward were erroneous and misleading, and would not now be accepted by any haematologist of the present day. Dr. Alexander Eddington, in a paper published in the British Medical Journal, 1890, (p. 1233,) gives an interesting account of the present state of our knowledge regarding the blood, and gives his own observations upon the subject. He shows the very varying sizes of the human red blood cells and the readiness with which this variation takes place. There is namely a distinct variation in the aggregate size between meals, the minimum occurring soon after a meal, while the maximum is seen at the end of a period of fasting. He also states the red blood corpuscles are diminished in size at the termination of an acute fever, after an exanthematous disease (such as scarlet fever or measles), while they are the largest during the fever. They are small in septic conditions, such as pyemia and erysipilas, which have lasted some time. F. Detmers (Proceedings of American Society of Microscopists, 1887, p. 216,) has given a valuable series of measurements of blood corpuscles, from which I extract the following, (Ibid, p. 219): "After carefully examining the specimens of blood I can assert, without fear of contradiction, that there can be no question but the blood of human beings can be readily distinguished from that of such animals as the mule, cat, calf, horse, etc., and still more readily from cattle, sheep, and pigs." Dr. Formad (Ibid, p. 20) calls attention to the great value of photographs taken of blood corpuscles under very high magnifying power, such as ten thousand diameters. Under such magnification the differences between the differences in sizes between those of man, dog, ox, sheep, and goat, become readily distinguishable by the naked eye. The following seems to me to represent the present state of our knowledge of blood stains from other stains with which we might be confounded: 1. Blood stains can be certainly and absolutely differentiated from stains produced by other colored fluids, by the presence or absence of the red blood corpuscles. 2. The blood corpuscles of birds, fishes, and reptiles, being oval and nucleated, can never be mistaken for those of human blood. 3. If the average diameter of the blood corpuscle in any specimen of blood (containing at least one hundred, and better five hundred corpuscles,) is less than 1-4000 of an inch, it cannot possibly be human blood. 4. If the blood corpuscles have an average diameter of from 1-3200 to 1-3300 of an inch, then it is human blood, (excluding the blood of the beaver, guinea pig, kangaroo, monkey, muskrat, porcupine, seal, or wolf.) None of these are domestic animals, and stains produced by their blood can scarcely ever be met with under such circumstances as to be confounded with stains of human blood. 5. The blood corpuscles of the dog 1-3580, rabbit 1-3662, ox 1-4200, pig 1-4250, horse 1-4310, sheep 1-5000, goat 1-6100, can, by the use of high magnifying power, and the careful counting of 100 to 500 corpuscles, be differentiated from human blood corpuscles, both in recently shed blood and dry blood stains. The late gifted Prof. Henry F. Formad replied under date of May 9, 1892, upon the subject, as follows: CLARK BELL, Esq. : 3535 Locust St., PHILADELPHIA, Pa., 5-9-'92. My Dear Sir :-I have written lately on blood and blood stains, but cannot lay my hands just now on these recent publications. I send you with this mail a copy of one of my monographs on blood and blood stains, which is the most complete one on the subject written either by myself or anyone else of late years. From the perusal of this monograph you will glean to your satisfaction what is known to the present day upon this intricate subject. Nothing new has been done on blood stains since the writing of this article. Our methods of investigating blood are, however, improving step by step with the improvement of the microscope and the modern appliances of the same. What was impossible to do ten or twenty years ago, viz: the distinction between the different size of corpuscles, is at present a comparatively easy matter. The older statements that human blood cannot be |