A green extractive matter, which comes in all vegetal bodies developed under sunlight, next deserves a place by itself, because it is one of the few organic bodies of which no rational analysis has ever been pretended. Though we can not state the constitution of this chlorophyl, we know that, except by turning acid in the stomach, it remains inert on the human system, as one might imagine would happen if he swallowed a bunch of green grass. _Lignin_, with which it is always associated, is mere woody fibre, and has no direct physical action. In no instance has any stomach been found to _digest_ it save an insect's--some naturalists thinking that certain beetles make their horny wing-cases of that. I believe one man did think he had discovered a solvent for it in the gastric juice of the beaver, but that view is not widely entertained. So far as it exists in opium it can only act as a foreign substance and a mechanical irritant to the human bowels. Next come two inert, indigestible, and very similar gummy bodies, _mucilagin and bassorine_. Sugar, a powerfully active volatile principle, and a fixed oil (probably allied to turpentine) are the only other invariable constituents of opium belonging to the great organic group of the hydro-carbons. I now come to a group by far the most important of all. Almost without exception the vegetable poisons belong to what are called the "nitrogenous alkaloids." Strychnia, brucia, ignatia, calabarin, woovarin, atropin, digitalin, and many others, including all whose effect is most tremendous upon the human system, are in this group. Not without insight did the early discoverers call nitrogen _azote_, "the foe to life." It so habitually exists in the things our body finds most deadly that the tests for it are always the first which occur to a chemist in the presence of any new organic poison. The nitrogenous alkaloids owe the first part of their name to the fact of containing this element; the second part to that of their usually making neutral salts with acids, like an alkaline base. The general reader may sometimes have asked himself why these alkaloids are diversely written--as, e.g., sometimes "_morphia,_" and sometimes "_morphine,_" The chemists who regard them as alkalies write them in the one way, those who consider them neutrals, in the other. Of these nitrogenous alkaloids, even the nuts of the tree, which furnishes the most powerful, _swift_ poison of the world, contains but three--the above-named strychnia, brucia, and ignatia--principles shared in common with its pathological congener, the St. Ignatius bean. Opium may be found to contain _twelve_ of them; but as one of these (cotarnin) may be a product of distillation, and the other (pseudo-morphia) seems only an occasional constituent, I treat them as ten in number--rationally to be arranged under three heads.