There is scarcely any position of more responsibility than that of the medical expert in cases of alleged poisoning. Often he stands with practically absolute power between society and the accused—the former looking to him for the proof of the crime and for the protection which discovery brings; the latter relying upon him for the vindication of his innocence. How profound and complete, then, should be his knowledge! how thorough his skill! how pure and spotless his integrity! how unimpeachable his results! Yet recently the humiliating spectacle has been repeatedly presented of expert swearing against expert, until the question at issue was apparently degraded into one of personal feeling or of professional reputation. So far has this gone that both judicial and public opinion seems to be demanding the abolition of expert testimony. The medical expert must, however, remain an essential feature in our criminal procedures, partaking as he does of the functions of the lawyer, inasmuch as he has, to some extent, the right to argue before the jury, partaking also of the judicial character in that it is his duty to express an opinion upon evidence, but differing from both judge and advocate in that as a witness he testifies to facts. Were the attempt made to do away with his functions, there would be an end to just convictions in the class of cases spoken of, because no one would be qualified to say whether any given death had been produced by poison or by a natural cause.
In many matters that come under the notice of medical experts there is room for honest differences of opinion. Of such nature are questions of sanity and insanity. It must be remembered that these are, after all, relative terms. Reason leaves its seat by almost imperceptible steps. Who can determine with exactness the line that separates eccentricity from madness—responsibility from irresponsibility? Moreover, the phenomena upon which opinion is based are, in such cases, so hidden, so complex, so obscure, that in the half-lights of a few short interviews they will often be seen differently by different observers.
In scarcely any of its parts does toxicology belong to this class of subjects—certainly not at all in so far as it deals with mineral poisons. To a great extent it is a fixed science—a science whose boundaries may be widened, whose processes may be rendered more delicate, but whose principles are in great measure settled for ever. Not in the imperfections of the science, but in the habits of the American medical profession and in the methods of our criminal procedures, lies the origin of the evils complained of.
Some of the causes of the present difficulties are readily to be seen. One is the common ignorance of legal or forensic medicine among the members of the profession. In none of our medical colleges is legal medicine taught as a part of the regular course or as an essential branch of study. Consequently, when the student graduates he has only heard a few passing allusions to the subject from professors of other branches. Unfortunately, this is more or less true of many other medical subjects of importance: helped out, however, by his mother wit, and impelled by necessity, the imperfectly-educated graduate after a time becomes very generally a skillful practitioner. During the period of growth his daily needs govern the direction of his studies, which are therefore more or less exclusively confined to the so-called practical branches. Forensic medicine is not one of these, poison cases are comparatively rare, and to be called upon to give a definite opinion upon such matters before a legal tribunal happens not once in the lifetime of most medical men. Consequently, to a great part of the American medical profession legal medicine is a veritable terra incognita.
Moreover, the whole drift of modern medicine is toward a division of labor, and forensic medicine is more widely separated from the ordinary specialties of the science than these are from one another. In a case of delicate eye-surgery who would value the opinion of a man whose attention had been devoted mainly to thoracic diseases? What specialist of the latter character would even offer an opinion? Yet physicians who acknowledge that they have paid no especial attention to toxicology do not hesitate to give the most positive opinions upon the most delicate questions of that science. Men who would, as in honor bound, ask for a consultation in any case of serious sickness outside of their line of private practice, on the witness-stand put forth with the utmost boldness their ignorant crudities, careless or forgetful of the fact that they may be imperiling the life of an innocent human being. On the trial of Mrs. Wharton for the attempted murder of Mr. Van Ness, Dr. Williams asserted that there are peculiar characteristic symptoms or groups of symptoms of tartar emetic poisoning;[13] and both he and Dr. Chew—who with frankness acknowledged that he had not especially studied toxicology—did most positively recognize tartar emetic as the sole possible cause of certain symptoms which were but a little beyond the line of medicinal action, and for which obviously possible natural cause existed. Contrast these bold opinions with the cautious statement of a man who had given a lifetime of study to this particular subject. On the trial of Madeleine Smith, Professor Christison—at that time the first toxicologist of England—stated that if in any case the symptoms and post-mortem appearances corresponded exactly with those caused by arsenic, he should be led to suspect poisoning.
Another source of mischief lies in the fact that the law does not recognize the well-established principles of forensic medicine, and consequently the books in which these principles are laid down by the highest authorities are excluded by the courts, while the vivâ voce evidence of any medical man, however ignorant on such points, is admitted as that of an expert.
It is therefore not to be wondered at that juries give but little consideration to the knowledge or professional standing of expert witnesses. It is, in fact, notorious that the medical autocrat of the village, who has superintended the entrance of the majority of the jurymen into this troublous world, is a more important witness than the most renowned special student of the branch: indeed, the chief value of the real expert often rests on his ability to influence the local physician.[14] At the late Wharton-Van Ness trial the defence desired to show that the work of the chemist employed by the prosecution was unreliable, because the analyses made by him in a previous case had "been condemned by the united voice of the whole scientific world." The court was not able to see the relevancy of this, and refused to allow the professional ability or standing of an expert to be called in question. The witness thus adjudged competent brought no results into court; had kept no laboratory notes; relied solely on a memory so deficient that although he had been teaching for thirty-five years, he could not tell the shape of a crystal of tartar emetic, the poison in question; and upon the stand made a statement different from one which he had furnished officially to the district attorney of Baltimore fourteen months before.
There are principles of toxicology which ought to have legal force and recognition, and ought to govern expert testimony in the same way that the principles of evidence govern ordinary testimony. Without presuming to enumerate these, I will cite two or three for illustration. Certain substances, the so-called irritant poisons, such as arsenic, tartar emetic and the like, induce their toxic effects by causing irritation and inflammation of the alimentary canal. All authorities agree that poisoning by these substances cannot be proved, or even rendered, very probable, by symptoms alone—that chemical evidence, the discovery of the poison in the food, dejections, or in case of death the body, is absolutely essential for making out a case. Irritation and inflammation of the alimentary canal occur so often and so suddenly from natural causes, which are sometimes apparent, but often hidden, that no especial weight can be attached to them.
In the case of the so-called neurotic poisons, those which act upon the nervous system, the symptoms are so closely simulated by natural disease that even when they agree in the most absolute manner with those usually developed by any such poison they only render poisoning highly probable, not certain.[15] When in any case the symptoms diverge from the typical array, poisoning becomes improbable just in proportion to the amount of divergence.
All toxicological authorities also agree that in the case of the metallic poisons, such as tartar emetic and arsenic, the metal must be brought into court, and that the so-called "color tests" are not to be relied on. When sulphuretted hydrogen is passed through solutions of these metallic substances colored precipitates are thrown down, which at one time were thought to be absolute proof of the existence of the poison in the original solution. But in the celebrated Donnal case, tried at Falmouth, England, in 1817, Dr. Neale saved the accused by showing that a decoction of onions, of which the deceased had eaten a short time before death, yielded similar precipitates to those relied upon by the prosecution as establishing the presence of arsenic in the stomach. In regard to tartar emetic, Dr. Taylor, in his work on medical jurisprudence, says: "Antimony in the metallic state is so easily procured from a small quantity of material that on no account should this be omitted. A reliance on a small quantity of a colored precipitate would be most unsatisfactory as chemical evidence." In defiance of all the authorities the prosecution, on the trial of Mrs. Wharton for the murder of General Ketchum, rested its proof of poison upon these color tests and their sequences. The defence, however, found that the counterparts of three out of the four so-called characteristic reactions were readily performed with the substances known to have been in the stomach of General Ketchum at the time of his death.