The third minor proposition repeats the rule of local access, which has already been enforced in treating of the fifth proposition. It was not necessary to maintain this in the case of medicines acting on the blood; but Neurotic agents must be shown to operate locally on the various nervous organs. I have only to repeat the arguments which were urged before. It is proved that the action of nerve-medicines cannot be propagated by nervous connexion, but that passage in the circulation is necessary; that the course of the latter is sufficiently rapid to account even for the action of Hydrocyanic acid; and that, however near a medicine be introduced to a nervous organ, it does not affect it unless it be allowed to reach it. The nerves are not naturally constituted for the conduction of medicinal impressions, but only for the passage of impulses of volition, sensation, or emotion. And this evidently forms a powerful safeguard to the system against the effects of a poison. The assertion is further maintained by the fact that the action of a Neurotic, when applied topically to the part which it tends to influence, is the same as that which is exerted by it on the same part after absorption. And lastly, some nerve-medicines have actually been found after death in the substance of those nerves and centres which had been affected by them during life.
The use of these medicines in the treatment of disease is defined in the fourth minor proposition. They have no influence in the blood. They are not employed in slow or long continuing diseases. Their applications depend on their known physiological tendencies, already stated. Abnormal deviations from the proper functions of the nervous system are rectified by means of the influence which they exert over the nervous organs.
When the powers of life are sinking, the nervous force on which life depends may perhaps be roused by a strong Stimulant, and maintained by its repetition. Sometimes the emergency may be thus postponed, and the danger escaped.
In violent inflammations and fevers, when the action of the heart is so violent, and the nerves that control it so excited, as to place life in peril, we may do good by the administration of a Sedative, such as Antimony or Digitalis, by which the nervous force may be reduced to its proper level.