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.
Gubler found phosphide of zinc remove the sensation of fatigue after hard work, improve appetite and digestion, and conduce to sleep. He gave a 1/2-gr. dose with an ordinary digestive pill at dinner-time; but such a dose is too large, and is very liable to nauseate. When the nervous system is jaded and below par, so that slight impressions are too deeply felt, and the nerve-controlling power is impaired, phosphorus has been found to supply what is wanting for a time; also, it has been said to improve intellectual tone in those subjected to either monotonous brain-work or to an unusual mental effort (Thompson). Dr. Broadbent early recorded some striking cases of this kind: one of "nervous break-down" in a city merchant, with insomnia, and extreme depression and incapacity for work, and another in which "epileptiform vertigo" was present in addition. Both got well "quickly and completely" under phosphorus (Practitioner, 1873).
In cases of Chronic Exhaustion of Brain-Power, or of general nerve-exhaustion consequent on chronic disease, small doses continued for a long time are advisable, and have been plausibly held to supply to the nerve-tissue a vital element in which it is deficient, and to improve its nutrition, just as Wegner showed that the drug improved the nutrition of bone; and certainly its supply, in some form, to nerve-tissue, is as necessary as that of iron to blood-corpuscles.
I have reason to believe that benefit may be obtained from phosphorus even when there exists evidence of atrophic change in the brain, of the nature of white softening or chronic fatty degeneration, with such symptoms as failure of memory and of self-control, loss of proper sensation and cerebral power generally. These are commonly associated with feeble heart-action, and with arterial degeneration, and may occur not only in advanced life, but as a consequence of wasting disease, chronic alcoholism, etc. I remember well a case of this kind in which epistaxis was a frequent symptom, and had proved rebellious to iron, acids, and other ordinary treatment in the hands of experienced men: small doses of phosphorus (ethereal tincture) improved the patient very much both as to brain and muscular power, but the symptoms always tended to recur on omission of the remedy, and he continued it for a long time with good results.
A suitable dose is 1/50 gr. thrice daily for about a fortnight, and then it should be reduced to 1/100 gr. or less, and should be taken for twelve to eighteen months, omission being made for about ten days in each month.
Although I do not find this experience to be general, yet it is not wholly singular, for Dr. Hammond also speaks of the value of the remedy in conditions of softening; he recommends similar doses given with cod-liver oil, or zinc phosphide in 1/10 gr. doses.