This section is from the book "Materia Medica: Pharmacology: Therapeutics Prescription Writing For Students and Practitioners", by Walter A. Bastedo. Also available from Amazon: Materia Medica: Pharmacology: Therapeutics: Prescription Writing for Students and Practitioners.
Since potassium chloride in the blood, in amounts above 1:10,000 slows and weakens the heart and retards the activity of other muscles, the potassium ion has been considered a muscle depressant. But in our food we ingest at least 1/2 ounce (15'gm.) of potassium salts daily, and if the diet is a purely vegetable one, sometimes as much as 3 ounces (90 gm.) daily. Dixon says that we do not get their specific action because they are excreted so rapidly by the kidneys, and Smilie has shown that ordinarily harmless doses of potassium chloride become severely toxic in those with chronic nephritis. It is probable that, other things being equal, the sodium salts should be preferred, unless cardiac depression is an object of the medication.