This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
These are remedies which insensibly change the functions or organization, without any necessary elevation or depression of the vital actions, and the influence of which is mainly recognized by their effects in disease. They may be stimulant or sedative, and they may produce various local effects which would rank them in other classes; but it is not through these that the special curative effects are produced, which entitle them to the name by which they are distinguished. Knowing so little of their mode of action, we are not possessed of grounds for subdividing them, and they therefore rank with the ultimate classes.