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.
Large doses of potassium salts lower the reflex irritability of certain parts of the spinal cord (Binz), but many observers consider this to be only secondary to depression of the circulation. The fall of temperature adduced is attributed to the same cause. In warm-blooded animals motor power is weakened, probably from a direct alteration in the chemical constitution of muscular elements, for electrical reaction remains. (On the other hand, Ramskill finds baths of sulphuret of potassium to be the most effective stimulant to muscular action during such diseases as wasting palsy - Medical Times, ii., 1860.) In healthy men a sense of weight and fatigue is often felt in the limbs after absorption of the more easily diffusible salts, as the nitrate, oxalate, chloride, iodide, or bromide; local anaesthesia of various parts of the body has been described as a result of drachm doses of bicarbonate (British Medical Journal, ii., 1876). There seems, however, to be some idiosyncrasy with regard to such effects, and although full doses usually depress the nerve-functions, Dr. Prout refers to pronounced nerve-excitement, and even convulsion in some cases, as connected with an excess of alkali, and the chlorate of potash is said to have caused headache and cerebral congestion (v. p. 272). Isambert considered it a nervine sedative, but "this action was not evident in healthy persons" (Medical Times, ii., 1856). Rabuteau finds the "perchlorate" to produce giddiness and other symptoms like those of quinine. Liquor potassae has been used to quiet the spasms of tetanus (Lancet, i., 1861).
Dr. Thompson traces the nerve-depression commonly caused by alkalies to an increased excretion of phosphoric acid under their use (v. p. 269).