Pain may be stopped by removing the cause of irritation, as, for example, by the extraction of a carious tooth or by rendering the nerveendings insensitive to irritation, as by the application of cocaine; by preventing its transmission along the spinal cord by antipyrin, phenacetin, acetanilide, cocaine, &c.; or by dulling the perceptive centre in the brain by means of opium or its alkaloids, by anaesthetics, and probably also, to a certain extent, by antipyrin and its congeners.
Quinine was the first antipyretic used, and after the introduction of such preparations as antipyrin and acetanilide it may still be said to be the safest, though it is much less powerful.
Anilides, compounds in which the amino group is substituted by an acid radical, are prepared by heating aniline with certain acids; antifebrin or acetanilide is thus obtained from acetic acid and aniline.
Phenacetin, acetanilide, phenazone and many similar bodies act as antipyretics in virtue of an action on the heat-regulating centres in the cerebrum.
When heated with aniline it yields phenol and acetanilide.