Now some of them tend in the end to act on the nerves or on the glands, not merely indirectly, but by bodily contact. But, whatever their subsequent action, they exert a primary and apparent influence on the blood itself. A little reflection will convince us that these remedies are more efficient than any others that can be selected out of the armory of physic. It is easy, and satisfactory for the time, to allay nervous excitement by employing a sedative, or by using a stimulant to communicate to the system a temporary strength. It is easy to knock down an inflammation, or to evacuate morbid humours, by stirring up the glands with a powerful eliminative. But these are all at the best but temporary measures. Unless the exigency be also of a temporary character, the disorder may soon return with unabated violence; again is the patient bowed down by its strong hand; again is the fatal termination seen looming in the distance but too distinctly. Then has the physician to call to his aid more potent means, remedies of more permanent and certain efficacy. The disease is in the blood--ever circulating, breeding, and destroying. It is there that it must be met; let the physician strike boldly and warily there, if he would effect a cure. These medicines, then, act in the blood. How they do so, and in what way they prove of use in the cure of disease, I shall next have to show, while attempting to prove the proposition in which I have briefly stated this mode of operation. Hæmatics are very numerous, and very important: I shall thus devote some space to their consideration. But I must first lay down a broad distinction between the two divisions of Hæmatic medicines. The diseases in which they are used appear all to originate in the blood, however they may manifest themselves. Now some of these diseases originate in a want of some principle or constituent of the blood, which want causes an aberration of the vital functions. Thus, in anæmia, there is a deficiency of the Hæmatosin of the blood corpuscles. In simple debility a want of a similar nature probably exists. In rheumatic fever and other disorders an excess of acid is formed and eliminated, possibly from a want of the alkali by which it should be neutralized. In common inflammatory fever there is an abnormal oxidation of the Proteinaceous compounds, possibly arising, as we shall see hereafter, from a failure of some principles which are the proper food of the oxygen. In diseases causing urinary deposits there is a want of those principles which should naturally retain them in solution. In typhoid fever there is said to be an excess of basic matter, and a deficiency of acid, in the blood. In pulmonary phthisis there is a deficiency of fat in the system. In the latter stage of malignant cholera there is an absence of watery particles in the blood. Some suppose that in scurvy there is a want of the salts of Potash in the blood.