The following table, by Dr. Pereira, will show at one view the principal characters of the crystalline constituents of opium :— The great pains now taken in the culture and preparation of Indian opium induce a preference for it over the other kinds. If Indian opium contain generally more narcotine, it is on that account perhaps better suited to cases in which the stimulating action is wished.
Good opium is not perfectly soluble in water ; Ath generally remains undissolved, consisting of the caoutchouc and resin. Constantinople opium, however, leaves no residuum of caoutchouc. When opium is entirely soluble in water, it may be suspected to have been prepared by boiling the bruised capsules and leaves, and it is of a very inferior kind. The specific gravity of good opium is 1.336, if great mechanical impu rities are not present. It is very inflammable, and burns with a clear flame, and forms a transparent alcoholic solution. Opium from the bruised capsules is not inflammable, and forms a turbid alcoholic solu tion. When gum arable or tragaeanth is used to adulterate it, the specimen forms, when rubbed with one part of alcohol and two of water, a tremulous gelatinous mixture.
It must be obvious that a substance of so complicated a nature cannot act uniformly on organised beings, even supposing them to be always constituted alike, which never is the case, since they vary according to age, constitution, habits of life, states of disease and idio syncrasy, &c. Some of the effects which follow the employment of opium have been attributed to one prinicple and some to another ; but, with a few exceptions, nothing positive has been ascertained. Morphia is by no means the only sedative principle ; and nareotinc, so long regarded as the stimulating principle, is, when pure, nearly if not quite inert. The odorous principle is unquestionably powerful, though it has no resemblance to hydrocyanic acid. The collectors of opium are generally pale and affected with trembling& If opium be heated, the odour evolved is fatal to animals, and persons have fallen down in a state of insensibility from breathing an air charged with the vapour of opium in some pharmaceutical processes.
It is most probable that the extractive and resinous principles, with the meconic acid, which seems to modify the properties of the morphia, are the stimulating ingredients of opium, and that the getting rid of some or all of these, as in the watery extract of opium, and a few of the secret preparations of opium, constitute the superiority of these preparations, as calmants, over crude opium, or the officinal preparations in which they are retained.
A most extensive series of experiments have been instituted to determine the effects of opium : on vegetables by Mareet and Macaire ; on animals by Charvet; and on man by numerous physiologists, including Charvet. From these it appears that opium acts as a poison to plants, by destroying their irritability. According to Charvet, in the case of the sensitive plant, where the opium failed to kilt the sub ject of experiment, and it slowly recovered its irritability, yet the further growth was completely stopped. " In the animal kingdom, Charvet tried its effects on mammals, birds, reptiles, amphibia, fishes, insects (both in their perfect and larval states), the annelides, the molluscs, polypiphera, and polygastrica, and found that it acted on all as a poison, but with somewhat different effects according to their organisation. Thus on man it may produce congestion of the brain (marked by sopor and apoplectic symptoms), or irritation of the brain and spinal marrow (indicated by convulsions and pain), or a sedative effect (manifested by paralysis).
In other mammals, two kinds of effects are seen for the most part ; the one of irritation, the'other of diminished nervous power, symptoms of congestion being altogether wanting or very slight. This differ ence of effect corresponds with a difference in the development of the brain.
in the invertebnated animals, no symptoms of irritation seem to be caused by opium. This poison in them acts only on the contractile tissues, and produces symptoms of weakness or loss of contractile power.
In the animal series, the action of opium varies with the degree of development of the nervous system ; and in the lowest orders the effects are quite analogous to those observed in vegetables. (Pereira.) (See Wilmer, ' Die Wirkung der Arzueimittel and Gifte in gesunden therischen Kiirper,' in which all the experiments are given in a classified arrangement.) Much disputation has taken place respecting the question, whether opium be a stimulant or a sedative, and most unnecessarily, as its action depends, in general, on the quantity taken, the frequency of repetition, and the state of the system when it is administered. That to persona in health, if the dose be small, it is a stimulant, seems unquestionable; and this is proved by the fact that the habitual opium•eaters consume it for the sake of its primarily stimulant effect, and not for the sake of the depression, languor, and suffering which succeed. The different degrees of action, resulting from a difference of dose, are so ably given by Dr. Pereira that they may be quoted here verbatim.