!66 THE STORY OF GERM LIFE. 



of the world has been almost purely empirical, 

 with a very little of scientific basis. Great hopes 

 are now entertained that these new facts will place 

 this matter upon a more strictly scientific foun- 

 dation. Certainly in the past twenty-five years, 

 since bacteriology has been studied, more has 

 been done to solve problems connected with dis- 

 ease than ever before. This new knowledge has 

 been particularly directed toward means of avoid- 

 ing disease. Bacteriology has thus far borne 

 fruit largely in the line of preventive medicine, 

 although to a certain extent also along the line 

 of curative medicine. This chapter will be de- 

 voted to considering how the study of bacteriol- 

 ogy has contributed directly and indirectly to 

 our power of combating disease. 



PREVENTIVE MEDICINE. 



In the study of medicine in the past centuries 

 the only aim has been to discover methods of 

 curing disease ; at the present time a large and 

 increasing amount of study is devoted to the 

 methods of preventing disease. Preventive medi- 

 cine is a development of the last few years, and 

 is based almost wholly upon our knowledge of 

 bacteria. This subject is yearly becoming of 

 more importance. Forewarned is forearmed, and 

 it has been found that to know the cause of a 

 disease is a long step toward avoiding it. As 

 some of our contagious and epidemic diseases 

 have been studied in the light of bacteriological 

 knowledge, it has been found possible to deter- 

 mine not only their cause, but also how infection 

 is brought about, and consequently how conta- 

 gion may be avoided. Some of the results which 



