This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
Ammonia salts, in medicinal doses, stimulate the general nervous system, probably by quickening circulation, but the special effect of large doses is exerted on the motor tract of the spinal cord, which is stimulated much in the same manner as by strychnia. Convulsions are produced, especially by strong intravenous injection, and as these occur equally when communication with the brain is severed, they are not cerebral in origin (Lange): neither do they start in the peripheral nerves, for they take place if the blood be cut off from these nerves by ligature (Funke): we conclude them, therefore, to be of spinal origin (Pfluger's Archiv., Bd. ix.), and section of the nerve-trunk of a limb stops their occurrence. Prostration follows the convulsive seizure, and a partial paralysis of the hinder limbs of animals (Rabuteau and Behier: Comptes Rendus, Soc. Biol., 1873). Spiegelberg made certain experiments in order to test the opinion of Frerichs that the convulsions of albuminuria were due to the circulation of ammonia carbonate, and when he had injected as much as 6 gr. of that salt into the veins of a dog, general convulsions occurred with clonic spasm and trismus, the pupil was dilated, general sensibility was reduced, and coma set in; after an hour and a half, free salivation and urination took place, and the animal recovered, remaining stupid for some time: larger doses caused vomiting, afterward, tetanus and coma; the vessels were found full of dark fluid blood (Lancet, ii., 1870). It is probable that ammonia is a direct and intense stimulant of respiratory centres in the medulla.
The full effects of chloride of ammonium are not often exemplified, but in the case of a lunatic who swallowed a large (unknown) quantity, there were vomiting, giddiness, shivering, depression, delirium, convulsion, and, later, collapse so complete as to simulate death: recovery was effected with galvanic and other powerful stimuli, and then tetanic spasms came on (C. Browne: Lancet, i., 1868). Temperature is raised under the physiological action of the chloride; lowered under the other salts.