Morphia is undoubtedly the main active principle of opium; but that it is not the only one is proved by the fact, that a certain quantity of opium produces a much greater effect than all the morphia which can be obtained from it, though it may be entirely exhausted. Thus, opium must be very good which will yield one part in ten of pure morphia. If the latter, therefore, were the only active principle of opium, one part of morphia should produce an equal effect with ten parts of opium; while, in reality, it is equivalent to no more than six parts. Which of the principles of opium it is that supplies this deficiency in the power of morphia has not been decisively ascertained. Nor are the effects of morphia precisely the same in character as those of opium. So far as I have been able to decide from observation and trial, I believe that morphia has precisely the same anodyne and soporific effects as opium, and closely resembles it in its stimulant influence on the brain. Like opium, also, it is apt to produce perspiration, though perhaps in a less degree; and is quite as much disposed to cause itching of the surface. But it is less stimulant to the circulation, less disposed to constipate, has less restraining effect on the secretions, and cannot be so well relied on for the suppression of morbid discharges. I am confident that it in general agrees better with the stomach, and is less apt to be followed by nausea, vomiting, and headache. It has appeared to me also to be less liable to provoke irregularities of mental action, and, with an equal excitant influence on the faculties and feelings, to derange them less frequently, and in a less degree.

Morphia itself is perhaps less certain in its effects than its salts; as, being insoluble or nearly so in water, it probably depends for its absorption, and consequent effects on the system, in some degree at least, upon the presence of acid in the stomach, and might operate more slowly, and feebly in the absence of acids. Hence it is that the salts are always employed, and morphia itself never. The salts most used are the sulphate, acetate, and muriate. So far as can be inferred from observation, there is positively no difference in the remedial effects of these salts upon the system; and one may be substituted for the other without disadvantage. All of them have one great advantage over opium, and those of its preparations the strength of which is determined by that of the opium, in their uniformity of dose. We know exactly how much of the narcotic principle we are giving when we prescribe a salt of morphia, while, in relation to opium, laudanum, etc., we are very far from this certainty, and may at one time give the medicine perhaps twice as strong as at another; for different parcels of opium, even bearing the same commercial name, not unfrequently have this diversity of strength.

The salts of morphia may be given in all cases in which the indication is to relieve pain, to procure sleep, or to quiet nervous irritation in any of its forms But they are less efficient as stimulants to the circulation in low forms of fever, and cannot be equally relied on for producing diaphoresis, for checking diarrhoea, or arresting profuse secretion or hemorrhage. They are preferable to opium in irritated states of the stomach, and in catarrhal affections, as they probably have less effect in producing dryness of the mouth and air-passages, and consequently in impeding expectoration. They often agree well with individuals on whom opium produces disagreeable effects. Thus, I have had under my care a female patient, whom a full dose of opium always kept awake during the whole night, but with whom the salts of morphia, in equivalent quantities, had their usual soporific effect. I believe, moreover, that there is less danger of giving them in over-doses. Though undoubtedly capable of fatal poisoning, they appear to be less so relatively than opium. A case was related to me by Dr. Charles Foulke, of New Hope, Pennsylvania, in which a woman took by mistake eleven grains of morphia, equivalent to about sixty-six grains of opium in anodyne effect, and yet recovered without having discharged any of the poison from her stomach. She became profoundly insensible, and during this state was delivered of a child, of the birth of which she was quite unconscious, and which survived. A case was recorded, some years ago, in one of the London journals, of which I made a note at the time, though I neglected to make the precise reference, in which a young man was believed to have taken somewhere between twenty and thirty grains of one of the salts of morphia, and yet escaped with life without evacuating measures, though the symptoms were very alarming.

Another advantage of the salts of morphia is the facility with which they can be applied endermically, and their great efficiency in this mode of application. They may be used in this way either for obtaining the general effects of opium, or to relieve some local affection, as neuralgic pain, and obstinate vomiting. Perhaps no remedy is more effectual, for the latter purpose, than one of the salts of morphia sprinkled upon a blistered surface in the epigastrium, denuded of the epidermis.

The salts of morphia are also specially fitted for the hypodermic method of administration; in other words, for injection into the subcutaneous areolar tissue, as recommended by Dr. Alexander Wood. In this method, they not only more rapidly and effectually relieve neuralgic pains in the neighbourhood of their application than by any other mode of using them, but also, according to Mr. Charles Hunter, of London, more quickly affect the system, and through this, even though applied at a distance from the seat of disease, remove the pain quite as effectually as if injected in its immediate vicinity. Sleep is induced by morphia thus used in a very short time, sometimes so soon as five minutes. In this mode of exhibition it is said to constipate less than when given by the mouth. Another advantage is that it can be administered, in some instances, where any other mode of exhibition is difficult or impossible. There are few affections in which opium is indicated, in which the salts of morphia have not been advantageously given in this way. Delirium tremens, violent adynamic delirium from whatever source, severe spasm of the diaphragm, stomach, and bowels, commencing tetanus, violent hysterical convulsions, and the eclampsia of puerperal women, are among the severer forms of disease in which it is said to have proved effectual. For the mode of using this and other medicines by hypodermic injection, the reader is referred to the general remarks on the subject, at page 78 of this volume. Unless under urgent circumstances, not more than about one-half of the dose should be given at first, which, under similar circumstances, would be required by the mouth for full effect; and it may afterwards be increased if found necessary. This caution has been rendered advisable by unexpectedly violent effects, which have sometimes originated from narcotic medicines administered hypodermically in ordinary doses. Any of the salts of morphia may be employed, and they should be given in solution; each dose being dissolved in from twenty minims to half a fluidrachm of water. Perhaps, on the whole, the acetate may be preferable, as least liable, when perfectly dissolved, to cause irritation.

The dose of either of the salts of morphia, equivalent in anodyne effect to a grain of opium, is, as near as I have been able to determine, one-sixth of a grain. One-eighth of a grain, I am quite sure, is less powerful than a grain of good opium; and one-fourth of a grain, I think, somewhat more so. Endermically, one-half of a grain may be used at first, and afterwards increased, if found necessary, to a grain or more. About one-third of a grain may be given, for a commencing dose, by enema, or as a suppository. Hypodermically, not more than a twelfth, or, at the outside, an eighth of a grain, should be administered as a beginning dose, under ordinary circumstances. As a liniment, morphia may be employed, dissolved in one of the fixed oils. The solution is most readily effected by first dissolving it in a little chloroform, and adding the solution to olive or almond oil.