(_a_) Opium and the remedies that resemble it are, for the treatment of neuralgia, fully represented by the hypodermic use of morphia, which is the only kind of opiate treatment that ought ever to be employed, save in very exceptional instances. The great reasons for the preference of the subcutaneous administration over the gastric are, the economy of the drug which it affects and the much smaller degree of disturbance of digestion which it causes. The hypodermic injection of morphia, if conducted on correct principles, enables us, when necessary, to repeat the dose a great number of times with but little loss of the effect, and consequently with a much smaller rate of progressive increase of the quantity required; and the absence of depressive action on digestion enables us to carry out simultaneously that plan of generous nutrition which has already been shown to be so important a part of treatment. Indeed, the case is hardly expressed with sufficient strength, when we say that hypodermic morphia is usually harmless to the digestive functions; for in a great number of instances it will be found actually to give an important stimulus both to appetite and digestion; and the patient, who without its aid could hardly be persuaded to take food at all, will not unfrequently eat a hearty meal within half an hour after the injection.
The remarkable effects of hypodermic morphia have, however, caused it to be rashly and indiscriminately used, and so much harm has been done in this way that it is necessary to be exceedingly careful in the rules which we lay down for its employment. Upon these grounds I must hope to be excused if, in order to render this work complete, I repeat a good deal of what I have already said in other places. In the first place, I shall speak of the mode of administration, and then of the dose.
As regards the mode of administration, I prefer the use of a solution of five grains of acetate of morphia to the drachm of distilled water; if the acetate be a good specimen, this will dissolve easily (and keep some time without precipitation) without the use of any other solvent. With a solution of this strength we require nothing elaborate in the form of the syringe; a simple piston arrangement does well; only it is advisable that the tube shall have a solid steel triangular point, and a lateral opening. As regards the place of injection, I must repeat the opinion[38] which I have already published, that Mr. Hunter's plan of injection at an indifferent spot is, in the great majority of instances, fully as effective as the local injection would be; nevertheless, there is one consideration which in some cases may properly induce us to adopt the latter plan. Very nervous and fanciful patients will sometimes be much more readily brought to allow the operation when it seems to go directly to the affected spot, when they would be sufficiently incredulous of the benefits of an injection performed at a distance to indulge their dislike of incurring pain by refusing to submit to it. And there is one class of cases in which it is likely that there are real physical advantages in the local injection; in instances of old-standing neuralgia with development of excessively tender "points," which are also the foci of the severest pain, it will sometimes be advisable to inject into the subcutaneous tissue at these points. There is undeniable reason for thinking that the sub-inflammatory thickening of tissues around a certain point of nerve delays the transit of the morphia into the general circulation, and enables it to act more directly and powerfully on the nerve, which it thus renders insensitive to external impressions; an important respite is thus gained, during which the nerve-centre has time to recover itself somewhat. At the same time it must be remarked that this immediate injection of a tender point is apt to be exceedingly painful, and it may be absolutely necessary to apply ether-spray before using the syringe. In early stages of neuralgia, before the formation of distinct tender points, there is no advantage whatever (except the indirect one above mentioned) in the local injection. And, on the other hand, it is often of great consequence not to run the chance of disfiguring such a part as the face, the neck, etc., when the injection can easily be done over the deltoid, or in the leg, or in some other part which even in women is habitually covered by the dress.