Most of the alkaline salts, whether neutral, or with excess of acid, are directly sedative to the circulation, independently of any evacuation they may produce. As a general rule, their sedative influence is not powerful, and is evinced rather by a reduction of temperature, than by any very striking effect upon the pulse. Hence they have been denominated refrigerants. Nevertheless, they do reduce the pulse both in frequency arid force; and some of them considerably so, especially nitrate of potassa. The probability is that they act through absorption, and, in part at least, directly upon the blood; impairing its quality, and consequently the functions which depend upon it for their due performance. The precise character of the change in the blood will be given, so far as it is known, when the several salts are specially considered. At present, it is sufficient to state that it is of a nature to render that fluid less capable of stimulating the circulation, and of supplying plastic material for nutrition. it is not impossible, however, that these medicines exert also an immediately depressing influence on the heart and blood-vessels, through their relation with the susceptibility of those organs. But all of the refrigerant salts have evacuant properties; some being specially cathartic, others diaphoretic, and others again diuretic; and it is more in reference to these properties, than to their direct sedative power, that they are remedially employed; though, in the choice of evacuant medicines, in any particular case, these are always preferred to others, when there is at the same time an indication to reduce arterial excitement and febrile heat. They will, therefore, be treated of severally in connection with the classes to which they belong as evacuants. Only one of them, which is employed chiefly as an arterial sedative, though possessed also of the property of stimulating the secretions, will be considered in this place.