IMPORTANCE OF HIGH POWERS. 53 



ment without being killed nay, there may be several 

 forms of organisms extremely minute which are at 

 present undiscovered, but which among other charac- 

 teristics possess the remarkable property of resisting 

 the destructive influence of a temperature of 300 or 

 350. From these many might afterwards grow. 



In many instances in which the absence of living 

 germs would have been inferred, minute organisms, 

 invisible by the aid of the magnifying powers usually 

 employed, have been discovered, and in considerable 

 number. And in some cases in which it has been 

 stated that living organisms were not present, there is 

 reason to think many might have been detected, had 

 greater care in the examination been exercised, and 

 higher magnifying powers employed. But though 

 this be admitted, the fact does not in the slightest 

 degree strengthen the case for the heterogenists. 

 They have to prove that living forms appear under 

 conditions which not only absolutely preclude the 

 possibility of the entrance of living germs from with- 

 out, but which ensure the death of every living form 

 that may have been present in the substances used 

 for experiment. The position is indeed a difficult 

 one, for the more investigation advances, and the more 

 we learn concerning the minute living germs which 

 exist in such wonderful profusion, the more do we 

 hesitate to place perfect confidence in the means 

 employed for the destruction of those that were 

 present before the experiment commenced, and for 



