Arsenic is a powerful antiperiodic, nearly rivalling quinine; it seems less serviceable than quinine in well-marked cases of ague, but is sometimes as good, or even better, than it in the irregular malarious manifestations such as headache, neuralgia, etc, which are known under the head of masked malaria. It is sometimes useful in chronic rheumatism and rheumatic gout, and in neuralgia of various sorts its effects are occasionally almost magical.

It has been used, not only in tic and hemicrania, but in spasmodic nervous diseases such as angina pectoris, chorea, and epilepsy, whooping-cough and asthma. It is often very serviceable in hay fever, and in cases of spasmodic sneezing coming on after exposure to dust or even without any apparent cause. It has been employed in chronic bronchitis with copious expectoration, and in ordinary catarrh without febrile disturbance. It appears to be very useful in the commencement of phthisis. Under its influence the author has seen consolidation of the lung, consequent on catarrhal pneumonia, clear up completely, even in a subject having a very bad family history.

Probable mode of action of Arsenic in Phthisis.

The treatment of phthisis is so important that it may be advisable to discuss in a few words the probable mode of action of arsenic and hypophosphites in its early stages. It is now probable that this disease depends on the presence of a bacillus (B. tuberculosis, p. 83). In order that it should grow within the body, however, it is necessary that a suitable nidus should be present, and the different susceptibility to the disease of different individuals, or of the same individual at different times, probably depends on their liability to present a suitable nidus. The Bacillus tuberculosis differs from such bacilli as the B. anthracis in being of a very slow growth, so that when it is cultivated artificially on a solid medium it takes about ten days before it succeeds in establishing itself and begins to grow. Consequently, when applied to an open wound, or when inhaled into the lungs of a healthy person, it does not, like the Bacillus anthracis, at once begin to multiply and produce disease in the organism, but it is usually removed by washing in the case of a wound, or by expectoration in healthy persons. But if its removal be interfered with it will produce disease. Thus, if instead of being applied to an open wound it be injected under the skin so that it cannot be removed by waashing, it will after a time begin to grow, and produce tuberculosis, first local and then general. It is probable that the case is similar in the lungs. In the healthy lung it finds no nidus, and is removed by expectoration, but if a portion of the lung be consolidated by catarrhal pneumonia, the consolidated part probably affords a nidus to the bacillus, and the longer the consolidation lasts the greater the risk of bacilli finding entrance. In croupous pneumonia the exudation into the alveoli, consisting chiefly of fibrin with a few leucocytes, quickly breaks up and is absorbed, so that it is comparatively rarely followed by phthisis. But the proliferated epithelial cells which fill the alveoli of the lung in catarrhal pneumonia are much more resistant; they break down and are absorbed much more slowly, and hence a much longer time is given during which bacilli may find a nidus. The marked hereditary nature of phthisis is a curious point in a disease which we suppose to depend on the presence of a bacillus, and is a character in which it differs from such diseases as anthrax, ague, or relapsing fever, which are also due to foreign organisms. But the difference probably depends on the slow growth of the tubercle bacillus, which renders a prolonged undisturbed rest at the point where it enters the body necessary for its further growth. The disease is not hereditary, but the predisposition to such morbid changes in the lungs as affords a nidus to the bacilli is hereditary.

The more rapidly the effused products in pneumonia can be removed from the lung, the less chance have the bacilli of finding a nidus. It is probable that arsenic, which causes fatty degeneration of the normal epithelial cells lining the alveoli, also causes a similar degeneration of such cells when filling the alveolar cavities. By thus breaking them up and quickening their absorption, arsenic will lessen the risk of bacilli finding a nidus in them and converting catarrhal consolidation into phthisis. Probably the hypophosphites act in a similar way. If the patient should be in places where there are no tubercle bacilli, "the consolidation may persist for a long time without phthisis occurring, and hence one advantage of sea-voyages in cases of recent consolidation.

Mode of Administration. - In those cases where the local action of arsenic on the stomach and intestine is desired, it is best to give it in small doses before meals, but where the action of the drug on other organs of the body is desired, it should be administered immediately after meals.

The symptoms which show that arsenic is beginning to produce its physiological effect, and that it is time to diminish the dose or cease its administration, are irritation of the eyes, with a pricking sensation in them, the conjunctivae being somewhat injected, and the patient showing a tendency to rub the eyes; or the digestive canal may be the first to show the effect of the drug, the tongue being covered with a thin white silvery fur, or red, with enlarged fungiform papillae; the appetite may fail, and colicky pains with a tendency to diarrhoea may appear before the eyes are affected. Either of these symptoms indicates that the drug should be discontinued, or the dose diminished.

In skin diseases arsenic is used more frequently than any other internal remedy. As it increases metabolism in the cells of the epidermis (p. 716) it is contraindicated in acute cases, or when there is any active cutaneous inflammation in a chronic case. It is sometimes useful in chronic eczema when associated with chlorosis, and in lupus, chronic urticaria, and the neuralgia following herpes zoster. According to Mr. Hutchinson it cures pemphigus. The skin-diseases, however, in which arsenic is most useful are psoriasis and lichen ruber; beginning with two minims of Fowler's solution three times daily, the dose should be gradually increased to 12 minims or even 30 minims daily, and it should be given until either the amendment begins, or the signs of conjunctivitis or gastric irritation appear. When these are noticed, the dose should be diminished until they become just perceptible, and the administration of the drug should be continued for some time after the eruption has disappeared, in order to prevent its recurrence.