ALKALOIDS, organic bases, forming defi nite salts with acids and resembling in some respects the metals of the alkalis, hence the name. A number of basic nitrogenous com pounds of marked physiological action and somewhat analogous in their chemical composi tion. It has been proposed to limit the word alkaloid to the group of basic nitrogenous prin ciples found in plants, the somewhat similar bodies found in animals being termed ptomaines (q.v.) and leucomaines (q.v.). (See ANIMAL ALKALOIDS). Some even class as alkaloids a series of feebly basic compounds prepared syn thetically from the anilines, antipyrine, etc. We shall here consider only such alkaloids as are basic nitrogenous principles, products of the metabolism of plants.
Distribution.— Alkaloids are widely distrib uted throughout the plant kingdom ; many plants contain them, and some plants contain a large Slumber; opium, Papaver sotnniferuns, for in stance, contains a dozen or more alkaloids. The Cinchona family also contains many. In such cases, however, the alkaloids are, as a rule, very closely related in their chemical structure. Cer tain plant families contain many, others a few or none. Most of the alkaloids are found in the Dicotyledons, a few only are found in the Monocotyledons, Colchicum, and perhaps some of the Lshacee The fungus Amanita muscaria contains the deadly alkaloid muscarine (q.v.).
The Papaveraceas, Solanacee and Rafsuacts /atm are particularly rich in alkaloids. The Legunsitiosee, Rubiacee, and Umbellifere con tain many, while the large families of the Com posite and Labiatee contain very few. For the most part similar alkaloids are found in re lated plants, yet a few widely separated plants contain similar alkaloids, berberin being an example. As to their location in the themselves, alkaloids are found mostly in the fruit and seeds; many are found in the barks, and some in the roots. They are formed for the most part in the actively growing portions of the plant and are probably katabolic products of the plant metabolism. They are usually found in solutions combined with some plant acid in the cell sap, sometimes dissolved in oils or inficil.tc, and in many instances are stored up in secretory passages in the plant. As to
the role that the alkaloids play in the plant economy it is difficult to state positively. They do not seem to be utilized by the plant as a source of energy and in some instances are even poisonous to the plant itself. One of the services they perform for the plant is to aid it in the struggle for existence by being poison ous to animals. The large quantities found in seeds is evidence of the support of this view.
For the most part alkaloids are solid, non volatile, crystalline bodies, a few being liquid and volatile, such as arecoline, nicotine, confine, spartein. The former contain carbon, hydro gen, nitrogen and oxygen. The three latter liquid alkaloids contain no oxygen and have a marked odor; the solid alkaloids possess no odor. With few exceptions the alkaloids are insoluble (or soluble with great difficulty) in water.
Chemically the alkaloids are divisible into five provisional groups, although it was at one time held that only those bodies belonging to the Pyridine group should be considered as alka loids. These groups as classed by Briihl are (1) the Pyrrolidine group — containing an alka loid from the coca leaf, hygrine; (2) the Pyri dine group, which contains a large number, pilo carpine, pilocarpidine, arecoline, arecaine, coniine, conydrine, piperine, nicotine, atropine, hyoscamine, cocaine, pelletereine, sparteine, cys tisine and others; (3) Quinoline group — con taining cinchonine, quinine, cinchonidine, strych nine, brucine, curarine, and others; (4) Ison group — containing the opium alkaloids, mor phine, papaverine, narcotine, codeine, thebaine, hydrocotarnine, hydrastine, cannabine, berber ine, corydaline; (5) alkaloids of undetermined relationship, a few only being of other than chemical interest, j ergotinine, colchicine, vera trine, cevadine, ervine, rubijervine, aspidos permine, yohimbine, anfialonine, luptnine,. gel semine, aconitine, pseudoaconitine, japacomune, dclphinine, emetine, etc. However, many alka loids. the structure of which is well known, such as caffeine, theobromine, muscarine, etc., do not fit into this scheme.