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Rh a paroxysm or two of one or two days' duration. The mildness of these attacks is probably explained by a partial immunity which has been conferred by previous attacks. For a summary of the symptoms evoked by the various strains of relapsing-fever spirochæte, see the Table on p. 242. Mortality.— The death-rate is usually below 6 per cent. In the feeble and old, death may take place at the height of the first paroxysm.

Diagnosis.— This disease is readily confounded with malaria, enteric, typhus, and influenza. The detection of the spirochætes with the microscope, or by animal injection, is the most reliable method of diagnosis. At an early stage the relapsing character of the clinical phenomena, not having declared itself, is not available as an aid to diagnosis, but at a later period the history of a fever which had relapsed about fourteen days from the commencement of the disease should be regarded as highly suggestive of relapsing fever.

Morbid anatomy.— The spleen is usually large and soft. Liver, kidneys, and heart show cloudy swelling. The skin in fatal cases is usually jaundiced, and there may be submucous petechue. The bonemarrow is hyperæmic. There is generally a marked polymorphonuclear leucocytosis. Treatment.— Ehrlich's discovery of the value of salvarsan in the treatment of syphilis naturally suggested that this drug would prove of use in the other spirochæte-caused diseases— yaws and relapsing fever. Fortunately the surmise has proved to be well founded. Intravenous injection of from 3 to 6 gr. of salvarsan and similar arsenicals in relapsing fever, after a short aggravation of symptoms is promptly followed by disappearance of the spirochætes from the blood and, in the vast majority of cases, recovery. Should relapse occur— a rare event— a second injection may be given. Atoxyl, so potent against trypanosomiasis, is useless in relapsing fever. Methods of administering salvarsan.— Salvarsan (dioxy-