It is customary to use oxygen in combination with chloroform, or nitrous oxide in order to produce insensibility to pain (see Anaesthetics).
Salmon also found that injury of a leaf by mechanical means, by heat, by anaesthetics, &c., would affect the immunity of the plant and allow infection by conidia which was not able to enter a normal leaf.
More volatile anaesthetics such as anestile or anaesthyl and coryl are produced by mixing with methyl chloride; a mixture of ethyl and methyl chlorides with ethyl bromide is known as somnoform.
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.
A clinical or therapeutical classification into such divisions as anaesthetics, expectorants, bitters, and so on, according to their practical applications, also leads to difficulties, as many drugs are employed for numerous purposes.