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.
In scabies, and in phtheiriasis, arsenic has sometimes been used, and a lotion containing a small proportion 1 with soft soap and spirit of wine has been much commended: it is painful in application, and has not seemed to me so good as other remedies; neither is the use of this substance free from danger, for an arsenical salve applied for scabies has produced poisonous effects.
For ascarides Trousseau recommended an injection of 1/5 gr. of white arsenic in 4 oz. of water; it is not often used, but would probably be effective. M. Boudin used the same remedy in larger doses, but it is unnecessarily dangerous.