A dose of Ipecacuan, by exciting the stomach, will abate both the force and velocity of the heart in its vital motion, and affect the whole series of blood vessels, from their origin to their most minute ramifications, as is evinced by the pallor of the skin under its operation, as well as by its efficacy in arresting hemorrhage; so the brain, when disordered by vertigo, frequently derives instantaneous relief from the administration of a tea-spoonful of æther in a glass of water. The stomach however is not in every case the medium of sympathy; a substance may excite a powerful impression upon a distant part, by the instrumentality of the nerves, without any concurrence of the stomach; thus, the _Belladonna_, by coming in contact with the _Tunica Conjunctiva_ of the eye, will occasion immediate dilatation of the _Iris_, although no other part of the system is in the slightest degree affected. But there is yet another mode by which remedies may be made to exert a sanative effect upon particular organs of the body, through the medium of what Mr. Hunter called _contiguous_ sympathy, and whose existence appears to depend upon the mere proximity and contiguity of parts, without any relation to the distribution of the nerves; thus it is, that relief is afforded to a deep-seated inflammation, by scarifying the nearest external surface; while we know from long experience that the thoracic or abdominal viscera, when similarly affected, receive corresponding relief from the same topical use of bleeding, blistering, or fomenting. With respect to the _Modus Operandi_ of medicines the following classification may be established. THE PARTICULAR ORGANS OF THE BODY MAY BE EXCITED INTO ACTION, THROUGH FOUR DISTINCT AND DIFFERENT MODES OF COMMUNICATION. I. _By the actual contact of the appropriate remedy._ 1. _Conveyed by absorption_, WITHOUT DECOMPOSITION. _Internally._│_a._ _through the branches of the Thoracic duct_. „ │_b._ _through the branches of the Vena │ Portarum_.[132] _Externally._│_c._ _through the branches of divided │ blood-vessels_. „ │_d._ _through the branches of Lymphatics_.[133] 2. _Conveyed by absorption_, WITH DECOMPOSITION, _by which one or more of its constituents are developed, and pass into the circulating current_. II. _By an impulse conveyed through the instrumentality of the nerves._ III. _By the sympathetic control exerted by the stomach on distant parts._ IV. _By the operation of contiguous sympathy, or of that which is excited by the mere proximity and continuity of parts._