THE MICROSCOPE AS A CRIMINAL DETECTIVE.

Globe, Volume III, Issue 259, 10 April 1875, Page 4

THE MICROSCOPE AS A CRIMINAL DETECTIVE.

[Scientific American,'] The annals of criminal jurisprudence furnish an abundance of cases in which the microscope, in the hands of an expert, has been the means of eliciting missing links in the circumstantial evidence pointing to the guilt of the accused. Instances are cited where the instrument has shown hairs, clinging to the edge of an axe, to be those of a human being, in direct contradiction of the statement of the prisoner, ascribing them to some animal ; and similar scrutiny of fresh blood upon clothing has proved the origin of the stain beyond a reasonable doubt. When blood, however, has once become dry, several authorities assert that it is impossible to distinguish it from that of the ox, pig, sheep, horse, or goat. It is urged that the differences between the average sizes of their corpuscles are too irregular to measure accurately, and that a man’s life should not be put in question on the uncertain calculation of a blood corpuscle’s ratio of contraction in drying. In opposition to these views are some recent experiments made by Dr Joseph G. Richardson, of Philadelphia. This investigation disposes of the first objection above mentioned by pointing out that, while it may be valid as regards feebly-magnified blood discs, it becomes void when these bodies are amplified 370 C times. Regarding the second, he stamps it as incorrect, and cites a case in which seven human blood discs, whose mean diameter had been accurately determined at l-3236th of an inch, were subsequently computed to average 1-3266, or only 1 -352292 of an inch less than their actual magnitude. Dr Richardson also points out, with reference to the last objection, that all the blood discs likely to be mistaken for those of man being normally smaller, instead of contracting they would have to expand to become conformed to those of human blood. This expansion does not occur, so that the only possible mistake in diagnosis would be to suppose that ox blood were present when man’s blood had actually been shed; so that at the worst we might contribute to a criminal’s escape, but never to the punishment of an innocent person. In order to afford a positive demonstration of the facts, Dr Richardson obtained, from each of two friends, three specimens of blood clots, from the veins of a man, an ox, and a sheep respectively, selected without his knowledge. By microscopical examination alone he was able to determine, with perfect accuracy, the origin of each sample. The corpuscles of human blood averaged 1'3430, with a maximum of 1-3174 and a minimum of T 3636 of an inch; those of the ox blood gave a mean measurement of 1-4662, with a maximum of 1-4347 and a minimum of 1-4874; while those of the sheep’s blood afforded a mean of 1-5952, with a maximum of 1-5405 and a minimum of T 6451 of an inch. From these and other experiments, Dr Richardson concludes that, since the red blood globules of the pig, ox, red deer, cat, horse, sheep, and goat “are all so much smaller than even the ordinary minimum size of the human red disc, as computed in my investigations, we are now able, by the aid of high powers of the microscope and under favorable circumstances, positively to distinguish stains produced by human blood from those caused by the blood of any one of the animals just enumerated; and this even after a lapse of five years (at least) from the date of their primary production,