12 THE STORY OF GERM LIFE. 



compound microscopes which made high powers 

 practical impossibilities ; and, above all, when we 

 appreciate the looseness of the ideas which per- 

 vaded all scientists as to the necessity of accurate 

 observation in distinction from inference, it is not 

 strange that the last century gave us no knowl- 

 edge of bacteria beyond the mere fact of the ex- 

 istence of some extremely minute organisms in 

 different decaying materials. Nor did the i9th 

 century add much to this until toward its middle. 

 It is true that the microscope was vastly improved 

 early in the century, and since this improvement 

 served as a decided stimulus to the study of mi- 

 croscopic life, among other organisms studied, 

 bacteria received some attention. Ehrenberg, 

 Dujardin, Fuchs, Perty, and others left the im- 

 press of their work upon bacteriology even before 

 the middle of the century. It is true that Schwann 

 shrewdly drew conclusions as to the relation of 

 microscopic organisms to various processes of 

 fermentation and decay conclusions which, al- 

 though not accepted at the time, have subse- 

 quently proved to be correct. It is true that 

 Fuchs made a careful study of the infection of 

 " blue milk," reaching the correct conclusion that 

 the infection was caused by a microscopic organ- 

 ism which he discovered and carefully studied. 

 It is true that Henle made a general theory as to 

 the relation of such organisms to diseases, and 

 pointed out the logically necessary steps in a dem- 

 onstration of the causal connection between any 

 organism and a disease. It is true also that a 

 general theory of the production of all kinds of 

 fermentation by living organisms had been ad- 

 vanced. But all these suggestions made little 

 impression. On the one hand, bacteria were not 



