These diseases, then, in some of which the want is proved, in others partly hypothetical, may be treated by medicines which supply the deficient matter, and thus restore a right state of things. They may supply it to the blood directly, or else cause it to be generated there. The former of these modes of restoration seems to be the most frequent, and may possibly, when we shall know more of such matters, be found to occur in all cases. This division of Hæmatics I have named Restoratives (Restaurantia.) Their action, as we shall see, is in some cases apparent, in others more obscure. They restore the blood directly to its proper condition, if there is only a deficiency, but they do not in general seem to have the power of counteracting any morbid or active material that may exist in the blood. Nor do they, except in large doses, exert themselves any peculiar action on that fluid. In these respects they differ from the other division of Hæmatics. They also differ in another important character. Each Restorative has in healthy blood a substance analogous to, or identical with itself: it replaces this when deficient. Not so with other Hæmatics. There is in general nothing in the blood corresponding to them--or if there be in some cases, they are not introduced with the intention of supplying its wants. Thus Restoratives may remain in the system, and are intended so to do; but these may not remain. They must pass out. In so doing they come under the head of Eliminatives, or that of Astringents. This is their secondary action, distinct from their primary and most important operation. What then is the curative action of these remedies? A large class of diseases depends on the presence in the blood of a morbid material, or, what amounts to the same thing, on the constant working of a morbid process in that fluid. Some of these, as the eruptive fevers, will run a certain course, and then come to an end. These we cannot generally stop, but can only alleviate. But others, more in number, and more commonly met with, tend naturally to run on for an indefinite period, unless by any means we can arrest their progress. Some depend on a contagious virus, communicable from one person to another, as Syphilis. Some, as Ague, are dependent on atmospheric or terrestrial influences. Others are due to some derangement of the secondary assimilative processes, as Scrofula, Scurvy, Gout, and Rheumatism. Others again, to causes that are ill understood, as convulsive disorders and skin diseases. Lastly, some may be caused in many different ways, as common inflammatory fever. Now the object in the treatment of such diseases is to obtain in each case some remedy, that shall be able to counteract this process, something that shall destroy the morbid influence at work, and thus restore health. Medicines that are used with this intention form the second division of Hæmatics, which I have named Catalytics (Catalytica,) from a Greek verb signifying to destroy or to unbind.