(From attenuo, to make thin). Attenuating medicines act, it is supposed, by diminishing the consistence of the blood, or secreted fluids, and almost exclusively of the fluids. Those which operate by immediate contact are few, and are water, or such as abound with water, as on this they depend for their action only. Yet water alone will not readily mix with the animal fluids, and it is often thrown out by the kidneys as an injurious substance, unless joined with farinacea or animal juices, so as to be submitted to the action of the stomach. Certainly, water is not alone an attenuant. It may be, however, doubted, whether the blood is in any instance too viscid; the buff coat in blood is owing to a very different state. If, however, the gluten is ever morbidly viscid, the neutral salts arc the only proper attenuants, and soap as containing an alkali may be such. The sweet fruits and sugar also produce some effect in attenuating the blood. The obstructions from more solid substances can never be attenuated by any fluid; and the only successful mode of treatment is, to excite the action of the vessels. Mercury may perhaps have some effect, but its influence in attenuating the fluids arises wholly from its increasing the action of muscular fibres of the sanguiferous system. See Hoffman, vol. i. and ii. cap. iv. Cullen's Mat. Med.