The right course lies in a combination of these various theories, embracing what is true and discarding what is erroneous in each of them, and supplying what may seem to be wanting in the whole. None of these ideas being by itself perfect, the sounder reasoners of the present day are driven to suppose that there are _various_ different ways in which medicines may _counteract_, and thus cure, different diseases. This _counteraction_ is distinct from _contrary action_; it may be direct or indirect; and it allows of any action in a medicine, tending to restore health, except an effect similar to the disease. Such a view was adopted by Dr. Cullen, the well known Nosologist, who lectured at Edinburgh towards the close of the last century. He discarded all special and confined views of the operation of medicines, believing that they acted in many and various ways, all of which tended to the same end--to counteract the influence of the disorder. This is well exemplified in his admirable directions for the treatment of fever, in which he enjoined the use of a number of different remedies, varied according to the nature of the case, and progress of the symptoms.[16] Dr. Pereira, the most learned and acute of living English writers on this subject, appears, like many others, to prefer a wide explanation of this description. On such views my own statements are based. I suppose that a disease in the blood is to be met by agents in the blood, which directly or indirectly counteract it there; that disorders, generally temporary, which depend on nervous derangement, are to be benefited by remedies which affect the nerves; and in the same way that a laxity of muscular fibre, or a failure in a secretion, should be treated by agents which especially possess the property of restoring to a right condition such parts or functions. Concluding, then, that it is impossible to account clearly for the actions of most medicines on _Mechanical_ or on _Chemical_ principles, we are led to infer that their influence must for the most part be _vital_ in its nature--that it must be such as could only be exerted in the living body. Even then we are unable to fix upon any single rule or formula which shall be capable of accounting for the actions of all at once. So it seems that the only general explanation which we can offer of the _modus operandi_ of medicines in the cure of diseases, is to say that they operate by _various counteractions_. This, then, introduces my Third Chapter. CHAPTER III. ON THE GENERAL MODES OF ACTION OF THERAPEUTIC AGENTS INTRODUCED INTO THE STOMACH. The principal affirmations which I have to make on this subject are divisible into Ten Propositions, as seen in the Table of Contents.