Administered internally in solution, it has a power of quickening the action of the heart, and exciting the circulation generally. It is therefore particularly useful in the common case of fainting, or threatened syncope. This stimulant power is possessed only by the free alkali and its carbonates. And as the secretion of the stomach is acid, Dr. Pereira supposes that the free or carbonated Ammonia becomes neutralized before absorption; that it is therefore unable to act in the blood except as a salt, and can only operate as a Stimulant while in contact with the coat of the stomach. Its influence must then be conducted by the nerves from the surface of the stomach to the heart. But though the nerves are the natural channels of various motor and sensory impressions, it is to assume an unprecedented thing to suppose that a medicinal action can be transmitted by their means to a distant part. For this and for other reasons it seems to me to be most likely that the solution of Ammonia is absorbed too fast in the stomach to be neutralized by the gastric juice. Or even if it were neutralized before absorption, it would probably be again set free on entrance into the blood, in which there is a slight excess of alkaline matter. Thus Ammonia would exist in the blood in a free state, except in those morbid conditions in which there is a general excess of acid in the system. I suppose the same to be the case with Potash, when it is given in any quantity. The great diffusibility of the free Ammonia would be an additional reason for its rapid absorption. When the gas is inhaled, as in the use of smelling-salts, and applied thus to the nasal and pulmonary mucous membranes, it must pass through to the blood in a free state, for these surfaces do not secrete an acid. And yet its effects in this case are the same as when it is taken into the stomach, which further renders it probable that in the latter instance it is absorbed free. When there is an excess of acid in the system, Ammonia may be used as a Restorative. It diminishes the acid reaction of the secretions by combining with the acid to form a salt. In ordinary conditions (_i.e._ when not required in the system) it has to be excreted from the blood. Both Ammonia and its salts act as Expectorants and Diaphoretics, being excreted on the mucous surface of the lungs, and on the skin. Free Ammonia is a better Expectorant than any of its neutral salts. The secretion of sweat contains an acid. The Ammonia which passes out on the skin combines with this acid. But on the pulmonary surface it is probably excreted free. For it is found that the careful inhalation of Ammoniacal gas has the same effect in augmenting the mucous secretion as the internal use of Ammonia. Ammonia is volatile, and soluble in air; and tends for that reason to pass off freely from those secreting surfaces which are immediately in contact with the atmosphere. (p. 278.)