INTRODUCTION. 29 c year Pasteur published a work upon Rouget dit Pore, and Loffler and Schiitz reported the discovery of the bacillus of glanders. In 1884, Koch reported the discovery of the "comma bacillus," the cause of cholera, and in the same year Iv6ffler discovered the diphtheria bacillus, and Nicolaier the tetanus bacillus. In 1892, Canon and Pfeiffer discovered the bacillus of influenza. In 1892, Canon and Pielicke first found the bacillus now thought to be specific for measles. In 1894, Yersiu and Kitasato independently isolated the bacillus causing the bubonic plague then prevalent at Hong-Kong. A new era in bacteriology, and probably the most triumphant result of the modern scientific study of dis- ease, was inaugurated in 1890 by Behring, who presented to the world the u Blood-serum therapy," and showed as the result of prolonged, elaborate, and profound study of the subject of immunity that in the blood of animals with acquired immunity to certain diseases (diphtheria and tetanus) a substance was held in solution which was potent to save the lives of other animals suffering from the same diseases.