In the course of a few hours, there is usually some indisposition, with a feeling of chilliness and slight rise of temperature; these symptoms pass off within twenty-four hours, and in a few days there is a decided improvement of health. Three or four days after an intra-muscular injection there may be pain and stiffness in the gluteal region. These preparations are the most efficient therapeutic agents that have yet been employed in the treatment of syphilis. The manifestations of the disease disappear with remarkable rapidity. Observations show that the spirochætes lose their capacity for movement within an hour or two of the administration, and usually disappear altogether in from twenty-four to thirty-six hours. Wassermann's reaction usually yields a negative result in from three weeks to two months, but later may again become positive. Subsequent doses of the arsenical preparation are therefore usually indicated, and should be given in from 7 to 21 days according to the dose. When syphilis occurs in a _pregnant woman_, she should be given in the early months an ordinary course of "914," followed by 10-grain doses of potassium iodide twice daily. The injections may be repeated two months later, and during the remainder of the pregnancy 2-grain mercury pills are given twice daily (A. Campbell). The presence of albumen in the urine contra-indicates arsenical treatment. It need scarcely be pointed out that the use of powerful drugs like "606" and "914" is not free from risk; it may be mentioned that each dose contains nearly three grains of arsenic. Before the administration the patient must be overhauled; its administration is contra-indicated in the presence of disease of the heart and blood vessels, especially a combination of syphilitic aortitis and sclerosis of the coronary arteries, with degeneration of the heart muscle; in affections of the central nervous system, especially advanced paralysis, and in such disturbances of metabolism as are associated with diabetes and Bright's disease. Its use is not contra-indicated in any lesion of active syphilis. The administration is controlled by the systematic examination of the urine for arsenic. _The Administration of Mercury._--The success of the arsenical preparations has diminished the importance of mercury in the treatment of syphilis, but it is still used to supplement the effect of the injections. The amount of mercury to be given in any case must be proportioned to the idiosyncrasies of the patient, and it is advisable, before commencing the treatment, to test his urine and record his body-weight. The small amount of mercury given at the outset is gradually increased. If the body-weight falls, or if the gums become sore and the breath foul, the mercury should be stopped for a time. If salivation occurs, the drinking of hot water and the taking of hot baths should be insisted upon, and half-dram doses of the alkaline sulphates prescribed.