This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
These are medicines which, by a direct influence, reduce nervous power, while they also depress the circulation. They appear to affect especially the organic nervous centres, without a peculiar direction to the cerebral functions; and bear to the cerebral sedatives a relation somewhat similar to that which, with an opposite mode of action, the nervous stimulants bear to the cerebral. It is not certainly known whether their sedative influence on the heart is direct, or exercised through the intervention of the nervous system; but, as there is a strong analogy in the operation of the several members of the class, and, in relation to digitalis and tobacco, experiment seems to have determined that their influence on the heart is secondary, the same is probably true of all.
Their effects on the system, and therapeutic application, will be most conveniently considered in connection with the several medicines individually. It will be sufficient here to say, in general terms, that they are indicated both in nervous irritation, and excessive action of the heart, and especially in diseases which combine these two morbid conditions. In inflammation, so far as the mere reduction of the circulation and nervous excitement is required, they are capable of rendering useful service; but as they do not, like bleeding and the arterial sedatives, directly change the character of the blood, they are less efficient as anti-phlogistics, and should be regarded rather as auxiliary than as principal remedies.