4. It is useful, however, to separate the meconic acid also; because, as its properties are more delicate, I have repeatedly been able to detect it satisfactorily, when I did not feel satisfied with the result of the search for morphia. Dr. Ure made the same remark in his evidence on the trial of Stewart and his wife. He detected the meconic acid, but could not separate the morphia. It may be detected in one of two ways,—by means of hydrosulphuric acid, or by sulphuric acid.
If the former method be chosen, suspend in a little water the precipitate caused by the acetate of lead (par. 2); transmit hydrosulphuric acid gas till the whole precipitate is blackened; filter immediately without boiling; then boil, and if necessary filter a second time. A great part of the impurities thrown down by the acetate of lead will be separated with the sulphuret of lead; and the meconic acid is dissolved. But it requires in general farther purification, which is best attained by again throwing it down with acetate of lead, and repeating the steps of the present paragraph. The fluid is now to be concentrated by evaporation at a temperature not exceeding 180° F., and subjected to the tests for meconic acid, more particularly to the action of perchloride of iron, when the quantity is small. If there is evidently a considerable quantity of acid, a portion should be evaporated till it yields crystalline scales; and these are to be heated in a tube to procure the arborescent crystalline sublimate formerly described. About a sixth of a grain of meconic acid, however, is required to try the latter test conveniently.
If the method of separating meconic acid by means of sulphuric acid be preferred, the precipitate formed by acetate of lead is to be treated with weak sulphuric acid, which forms insoluble sulphate of lead, and disengages the meconic acid. The liquid obtained by filtration is then to be evaporated as above, to obtain crystals, which are to be examined by the tests for meconic acid. Orfila thinks this method more delicate than the mode by hydrosulphuric acid gas. I am inclined from my own experiments to doubt his statement.
5. If there be a sufficiency of the original material, Merck’s process for detecting porphyroxin may be tried [see p. [534]]. But I doubt whether this process is sufficiently delicate for medico-legal purposes.
I wish I could add my testimony to the opinion, expressed on a remarkable occasion by Professor Chaussier, in favour of the delicacy of the tests for morphia and its compounds, that they might be detected “jusqu’à une molécule.”[[1685]] In one sense this statement may be correct. Morphia, separated from the complex mixture of principles with which it is combined in opium, may be detected in extremely small quantities. Accordingly, M. Lassaigne has supplied, for the discovery of acetate of morphia in mixed fluids, an excellent process, whence the chief part of the three first paragraphs of the preceding method for opium are borrowed; and from the facts stated by him in his paper,[[1686]] as well as from the experimental testimony of Professor Orfila,[[1687]] it appears that Lassaigne’s process will furnish strong indications, if not absolute proof of the presence of that salt, in the proportion of two grains to eight ounces of the most complex mixtures. Hence the search for acetate of morphia in a suspected case is by no means hopeless. But the detection of acetate of morphia is an object of small moment, compared with the detection of morphia in its natural state of combination in opium. Now my own observations lead me to entertain serious doubts, whether the best method of operating hitherto known could be successfully applied to the detection of the equivalent opium in complex mixtures. By the process I have recommended it is easy to procure, from an infusion of ten grains of opium in four ounces of water, satisfactory proof of the presence of morphia by the action of ammonia, perchloride of iron and nitric acid, and equally distinct proof of the presence of meconic acid by perchloride of iron, as well as sulphate of copper. But on proceeding to apply the process to organic mixtures, I have found that when the soluble part of ten grains of opium was mixed with four ounces of porter or milk, I could develope no property of morphia but its bitterness, and no indication of meconic acid but the action of perchloride of iron. MM. Larocque and Thibierge, it is right to add, have in similar circumstances found the process somewhat more delicate.[[1688]]
It is of great consequence, however, to remark, that in cases of poisoning with opium, the medical jurist will seldom have the good fortune to operate even upon so large a proportion of the poison as in my experiments; because the greater part of it disappears from the stomach before death. This will not happen always, as may be seen from various cases mentioned afterwards in the section on the morbid appearances caused by opium. But, according to my own observations, the poison will often disappear in a short time, so far as to render an analysis abortive. Thus in the case of a young woman who died five hours after taking not less than two ounces of laudanum, I could apply to the fluid, procured from the contents of the stomach, by paragraphs 1, 2, and 3 of my process, only the test of its taste, which had the bitterness of morphia. In the case of another young woman, whose stomach was emptied by the stomach-pump four hours after she took two ounces of laudanum, I could obtain from the evacuated fluid, when properly prepared, only the indications of the presence of morphia supplied by its bitterness and the imperfect action of nitric acid,—and the indication of the presence of meconic acid supplied by the imperfect action of perchloride of iron. In a third case, where the stomach was evacuated two hours after seven drachms of laudanum had been swallowed, even the first portions of fluid withdrawn had not any opiate odour, and did not yield any indication of the presence even of meconic acid. Now, on the one hand, the quantity taken in these instances is rarely exceeded in cases of poisoning with laudanum; and, on the other hand, the interval during which it remained in the stomach subject to vital operations is considerably less than the average in medico-legal, and above all in fatal cases. It may be laid down, therefore, as a general rule, that in poisoning with opium the medical jurist, by the best methods of analysis yet known, will often fail in procuring satisfactory evidence, and sometimes fail to obtain any evidence at all, of the existence of the poison in the contents of the stomach. In a case published by Dr. Bright from the experience of Mr. Walne of London, it is stated that the matter removed from the stomach only half an hour after an ounce and a half of laudanum had been taken, while the stomach was empty, did not smell of opium.[[1689]] This case is quoted to put the reader on his guard. But at the same time it does appear extremely improbable that the whole opium had disappeared from the stomach in so short a time, and much more likely that it might have been found by analysis in the matter first withdrawn.
I have taken some pains to establish the proposition laid down above, because in a matter of such importance it is always essential, that the medical inspector know the real extent of his resources; and it has appeared to me that, greatly as the hand of the chemist has been strengthened by late discoveries in vegetable analysis, his power has been overrated both by his scientific brethren, and by the medical profession generally. I am happy to find, since the first publication of these remarks, that they coincide with the experience and opinion of so eminent an authority as Professor Buchner; who has observed that a chemical analysis must often fail to detect opium where there could be no doubt of its having been administered in large quantity.[[1690]]
It is of moment to add, that in two of the instances mentioned above the odour of laudanum was perceived in the subject of analysis,—faintly, however, and only for a few hours after it was removed from the stomach. Although the peculiar odour of opium is a delicate criterion of its presence, it does not follow that it should be preferred to an elaborate chemical analysis. For it is a test of extreme uncertainty. There is in the contents of the stomach such a complication of odours, that with a rather delicate sense of smell, I have sometimes been unable to satisfy myself of the presence of the opiate odour where others were sure it existed. At the same time the medical jurist should not neglect it as a subsidiary test. It is always strongest and most characteristic, first, when the stomach is just opened, or the contents just withdrawn, and again, when the fluid, in the course of preparation, as directed in paragraph 1 (p. [535]), is just reaching the point of ebullition. The latter odour is somewhat different from the former, yet quite peculiar, and such as every chemist must have remarked on boiling an infusion of opium. It is further to be observed, that although the odour of opium is a very delicate test of its presence even in complex organic mixtures, chemical analysis may be successful, where this character fails. Dr. Morehead of the Bombay service, in applying my process to the fluid withdrawn by the stomach-pump, detected morphia both by nitric acid and perchloride of iron, although he could not detect any odour of opium in the fluid.[[1691]]
So much for the delicacy of the process. As to its precision,—from what I have myself witnessed, as well as from the experience of Dr. Ure, it will often happen in actual practice, that the only indication of opium to be procured by the process consists in the deep red colour struck by perchloride of iron with the meconic acid. Now, will this alone constitute sufficient proof of the presence of opium? On the whole, I am inclined to reply in the affirmative. Sulpho-cyanic acid, it is true, has the same effect, and this acid has been proved by Professors Gmelin and Tiedemann to exist in the human saliva,[[1692]]—a fact which was called in question by Dr. Ure in his evidence on the trial of the Stuarts, but which at the time I had verified, and which Dr. Ure has since been compelled by experiments of his own to admit.[[1693]] But it must be very seldom possible to procure a distinct blood-red coloration from the saliva, after it has been mixed with the complex contents of the stomach, and subjected to the process of analysis detailed above;[[1694]] and the check proposed by Dr. Percy (p. [532]) will distinguish it.