ioo INFECTION AND IMMUNITY 



virulence, and that in every infectious disease mild 

 cases may occur, not only because of the slight sus- 

 ceptibility of the individual, but also because of the 

 "attenuated" virulence of the specific germ. In the 

 eighteenth century, the beginning of sanitary science, 

 isolation of the sick, and seaboard quarantines came 

 to the aid of these natural agencies, and did much in 

 the way of arresting the progress of this pestilential 

 disease. At the present day these measures, together 

 with disinfection by heat or chemical agents, are 

 relied upon by sanitarians with great confidence as 

 being entirely adequate for the exclusion of this 

 disease or for stamping it out if it should effect a 

 lodgment in localities where an enlightened public 

 sentiment permits the thorough execution of these 

 preventive measures; but when the disease prevails 

 among an ignorant population which strenuously ob- 

 jects to the carrying out of these measures, the con- 

 test between the sanitary officer and the deadly germ 

 is an unequal one, and the stamping out of an epi- 

 demic becomes a task of great magnitude, if not 

 entirely hopeless. This is illustrated by the experi- 

 ence of the English in their encounter with bubonic 

 plague in their Indian Empire. 



Plague seemed to be almost a thing of the past 

 and no longer gave any uneasiness in the countries 

 of Europe which had formerly suffered from its rav- 



