It will be seen that the first minor proposition affirms them to be Hæmatic medicines, according to the definition given before. The second is required; for if there were not a necessity in the blood for substances like them, they could supply nothing. The third also is necessary, for if they were excreted in all cases, it is evident that their Restorative action could not be lasting. An exception must be made in the case of those that are used to supply something which is necessary in order that a secretion may be properly elaborated. Medicines of the Sixth Order are particularly used with this intent; as also some acids and alkalies. But these are not repugnant to the blood, like Catalytics. In the fourth place it is affirmed that being thus fitted for the blood, and allowed to remain in it, they tend to cure a disease which depends on the want of a substance similar in nature to themselves. After giving a brief account of each of the orders of Restoratives, it will be my object to prove that these affirmations are severally applicable to each of them. ORD. I. ALIMENTS. An article of food is the simplest form, and in fact the type, of all medicines of this division. Out of the materials of the food the whole blood is constantly elaborated, and all the tissues are constructed. Aliments were divided by Dr. Prout into four kinds:--(1) Aqueous; (2) Albuminous; (3) Saccharine; (4) Oleaginous. These kinds differ much in chemical conformation. The second kind alone contain Nitrogen. The last two are both called _carbonaceous_; but those of the fourth kind contain more Carbon than those of the third. The following will serve to illustrate the differences in the chemical composition of these groups. 1. Water = H O 2. Proteine = C_{40}H_{31}N_{5}O_{12} 3. Starch = C_{10}H_{10} O_{10} 4. Stearic Acid = C_{68}H_{68}O_{7} Water is useful in dissolving the other elements, and reducing them to a state of solution which is fitted for the formation of blood, and of the other fluids of the body. We have already seen in what way these various matters are dissolved and absorbed in the _primæ viæ_, and how they pass into the circulation; that Proteinaceous and Saccharine matters pass into the capillaries of the Portal vein, and thence onwards through the liver; and that fatty matters are reduced to a kind of emulsion by the intestinal juices, and pass through the lacteals into the thoracic duct, by which they are conducted into the circulation at large. What then are the chief uses for which these matters are required in the system, and what great functions do they fulfil?