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.
Dr. J. B. Andrews and many others find phosphoric acid to be a powerful nerve-tonic, but the conclusions are founded more upon clinical observations on depressed persons than on the healthy. "Moderate doses produced on the latter the feeling of buoyancy and exhilaration already mentioned, but larger quantities caused a feeling of drowsiness, an inclination to lie down, and unwillingness for mental labor." The acid exerts also a marked control over the vaso-motor nerves, and through them improves the tone of the circulation. Hecker and Burdach concluded that phosphoric acid acts more than any other on the nervous system, heightening excitability in a great degree. Sundelin asserted that this action is directed especially to the genital organs, and although neither Neligan nor Andrews could verify this, I have myself noted it in sixteen patients, who had no knowledge of the supposed aphrodisiac quality of the drug; they all complained to me of such effects in greater or less degree.