First, those whose action is merely acrid--so far as known expending themselves upon the mucous coats. (_Pseudo-morphia_ when it occurs belongs to these.) So do _porphyroxin; narcein_; probably _papaverin_ also; while _meconin_, whose acrid properties in contact with animal tissue are similar to that of meconic acid, forms the last of the group. The second head comprises but a single alkaloid, variously called paramorphta or thebain. (It may interest amateur chemists to know that its difference from strycchnia consists only in having two less equivalents of hydrogen and six of carbon--especially when they know how closely its physical effects follow its atomic constitution.) A dose of one grain has produced tetanic spasms. Its chief action appears to be upon the spinal nerves, and there is reason to suppose it a poison of the same kind as nux vomica without the concentration of that agent. How singular it seems to find a poison of this totally distinct class--bad enough to set up the reputation of any one drug by itself--in company with the remaining principles whose effect we usually associate with opium and see clearest in the ruin of its victim! The remainder, five in number, are the opium alkaloids, which act generally upon the whole system, but particularly, in their immediate phenomena, upon the brain. I mention them in the ascending order of their nervine power; narcotin; codein; opianin; metamorphia, and morphia. The first of these the poppy shares in common with many other narcotic plants--tobacco the most conspicuous among the number. In its anti-periodic effects on the human system it has been found similar to quinia, and it is an undoubted narcotic poison acting on the nerves of organic life, though, compared with its associates in the drug, comparatively innocent. The remaining four act very much like morphia, differing only in the size of the dose in which they prove efficient. Most perfectly fresh constitutions feel a grain of morphia powerfully; metamorphia is soporific in half-grain doses; [Footnote: American Journal of Pharmacy, September, 1861.] opianin in its physical effects closely approximates morphia; codein is about one-fifth as powerful; a new subject may not get sleep short of six grains; its main action is expended on the sympathetic system. It does not seem to congest the brain as morphia does; but its action on the biliary system is probably little less deadly than that of the more powerful narcotic.