10 INTRODUCTION 



studied the blood of animals sick with anthrax and compared it with 

 that of healthy ones. He discovered the anthrax bacillus. This work 

 was extended by Davaine, Pasteur, Koch, and others, and from this, 

 the science of bacteriology has been developed. The particulate causes 

 of many infectious diseases have been recognized, isolated, and their 

 effects on animals demonstrated. Many of the mysteries of contagion 

 have been revealed and the conditions of the transmission of disease 

 made known. The fundamental principles of preventive medicine have 

 been developed into a science which is to-day the most potent factor 

 in the progress of civilization. Finlay suspected a certain mosquito 

 to be the carrier of the virus of yellow fever. Reed and his co-workers 

 demonstrated the truth of this theory, the work of Gorgas has freed 

 Havana from the pestilence, and the construction of the Panama Canal 

 is an accomplished fact. 



Laveran discovered Plasmodium malariae. Ross studied its life his- 

 tory, and the fetters of a disease that has so long retarded the progress 

 of man, have been broken. Mitchell and Reichert investigated the 

 poisonous properties of snake venom. Sewall immunized animals with 

 it. Ehrlich studied the similar bodies, abrin, ricin and diphtheria 

 toxin, and von Behring and Roux gave the world antitoxin, the 

 magical curative value of which has greatly reduced the mortality 

 from diphtheria. The experiments of Villemin demonstrated the con- 

 tagious nature of tuberculosis, long suspected and frequently denied. 

 The diligent research of Koch resulted in the recognition and isolation 

 of the causative agent, and since this discovery the mortality of the 

 Great White Plague in Europe and the United States has been dimin- 

 ished more than half. It is, then, within the range of sanity to look 

 forward to the time when the former "Captain of the hosts of death" 

 will be known only by the fearful records he once made in the history 

 of man's struggle to be relieved from the heavy tribute paid to 

 infection. 



We boast of a great civilization, but this is justified only within 

 limits. Science more nearly dominates the world than at any time in 

 the past. Learning permeates the masses more deeply, but credulity 

 and ignorance are widely prevalent. In this country of nearly one 

 hundred millions, there are thousands whose greed impedes the prog- 

 ress of the whole, tens of thousands whose ignorance retards their 



