This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
Arsenous acid has no action on the skin, but applied to raw surfaces it is a powerful caustic.
Alimentary canal. - Unless the dose be very small all preparations containing arsenic are very severe gastrointestinal irritants (see Toxicology). Part at least of this effect is due to excretion of the arsenic into the stomach after absorption, for if given subcutaneously there may be no local effect, although there is intense gastritis soon after injection. In minute doses they are gastric stimulants, causing dilatation of the gastric vessels and an increased flow of gastric juice. Small doses also stimulate the duodenum.
Arsenic is absorbed into the blood. Nothing is known of its physiological action there; but it can, in some forms of anaemia, increase the haemoglobin and the number of red corpuscles. Given to animals it considerably increases the red marrow at the expense of the yellow, and slightly stimulates the formation of compact bone.
In the frog the rapidity and force of the heart are lessened till it finally stops. This is a local action, for it takes place when applied to the excised heart. Large doses destroy the capillaries and lead to haemorrhage.
In many diseases arsenic evidently profoundly affects metabolism, for the patient recovers under treatment by this drug. It is doubtful whether, if given in small doses to healthy persons, it usually does more than sharpen the appetite. It has been stated by Dogiel to unite with albumin; another view, that of Binz and Schulz, is that arsenous acid becomes arsenic acid by taking oxygen from the protoplasm, but that the arsenic acid subsequently yields up the oxygen again, and that the activity of arsenic is due to its being a carrier of oxygen. Some of the people in Styria eat white arsenic in small quantities, and it increases their strength, weight, and appetite, and clears their complexion. It is probable that the reason why these people can take arsenic in such quantities is that an antitoxin is developed in them. Wood concludes that small doses of arsenic check tissue change and decrease nitrogenous elimination, whilst toxic doses have the opposite effect. But there is no proof of any of these statements, and we have no certain knowledge of the influence of arsenic on nutrition, nor do we know of any action to which its beneficial effects in many diseases can be referred; but as the drug certainly in some way alters the condition of the sufferer it is vaguely called an alterative. It is eliminated by the urine, the alimentary canal, the sweat, the saliva, the milk, and even the tears, but it is also stored in the body, chiefly in the liver and kidneys. It may be found many years after death in the bodies of those who have taken it during life. It can pass from the mother to the foetus.