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X] According to Thomas, in from three to seven hours an adequate dose of atoxyl causes the trypanosomes to become swollen, deformed, and almost motionless, their cytoplasm taking on a peculiar ground-glass appearance, becoming vacuolated, and presenting large dark granules. After seven or eight hours, coincidently with a marked increase of leucocytes—— especially phagocytes—— the parasites become rapidly fewer, and by the sixteenth or eighteenth hour completely disappear. Arsenic, in the form of Fowler's solution or of orpiment, is sometimes given by the mouth; but this way of administering the drug, especially in Europeans, has been quite superseded by the intramuscular injection of a variety of relatively feebly toxic preparations, including atoxyl, soamin, arseno-phenylglycin, arsacetin, salvarsan,* etc.

Atoxyl, a meta-arsenic-anilin compound, introduced by Thomas, is probably the best of these, and the one most usually employed. Unfortunately it has one serious drawback—— in large doses it is apt to give rise to optic neuritis, arid consequent atrophy and blindness. The drug, therefore, must at once be stopped on the slightest threatening—— dimness of vision or congestion of the disc—— of such a calamity. Gastro-iiitestinal irritation and peripheral neuritis are also indications that it has to be suspended, at least temporarily, arid the subsequent dose reduced. Atoxyl is best given intramuscularly in 10 per cent, solution in sterile normal saline. The solution should be freshly made and free from precipitate. The individual dose should not exceed 7 or 8 gr. The practice as regards dosage and the times and frequency of administration varies. Some advocate a 7-gr. dose once every fifth day until symptoms subside. After a few weeks, similar courses, lasting for a month and repeated at short intervals, are kept up for at least one year. My practice has been to give an injection of 3 gr. every third day, and to keep this