In a lesson of this kind it is impractical to classify all drugs accurately according to their chemical nature. For convenience of the student, however, the drugs commonly used in medicine will be divided into three groups, which have common representatives, and whose general effect upon the human body are well understood. These three groups are: a Alkaloids and narcotics b Alcohols and related compounds c Poisonous mineral salts and acids a ALKALOIDS AND NARCOTICS [Sidenote: Effect of alkaloids upon the body] All alkaloids are of vegetable origin. They all contain nitrogen, and in some respects resemble ammonia. Many of the alkaloid compounds are used in medicine. They affect primarily the nervous system, and may cause freedom from pain, or that abnormal state of exhilaration of which the cocain addict is a typical representative. Substances of this alkaloid group doubtless have useful functions in the plant in which they grew, but in the animal body they are disturbing factors. Among the most important alkaloids may be mentioned opium, cocain, nux vomica, and quinin. OPIUM [Sidenote: Composition of opium] Opium is the evaporated sap that flows from incisions made in the unripe capsules of certain Asiatic species of poppy. It contains a large number of chemical compounds which belong to the alkaloid group. The chief alkaloids in opium are codein, narcotin, heroin, and morphin, the most active being heroin. Other alkaloids are of similar composition. The general effects and the uses of the crude opium and the refined morphin may be considered together. The latter, being more concentrated, is used in much smaller quantities. [Sidenote: Effect of opium] The effect upon the body of either opium or of morphin is that of benumbing the nerves and producing sleep. Opium illustrates in a typical manner the progressive stages by which both the body and the mind may become enslaved to the influence of a narcotic. The last stages of the opium or of the morphin slave is probably the lowest state of depravity into which the human being can sink. [Sidenote: Origin of the morphin habit] Opium is eaten or smoked by the Chinese and by other Asiatic races to a very great extent. This habit is considered the worst form of slavery to drugs that is known except cocain. In this country the morphin habit is the more common form. Morphin is either taken internally or is injected beneath the skin by a hypodermic syringe. It is estimated that the great majority of the morphin slaves in this country begin the use of this drug under "their" doctor's prescription. [Sidenote: The several uses of morphin]