THE HISTORY OF BACTERIOLOGY. 441 



rior god or patron of the invisible or visible poi- 

 sonous flies that brought disease. The Roman 

 writer Varro supposed in like fashion that, as 

 we recognize with the naked eye both large 

 and small insects hovering over the marshes, so 

 insects still smaller are able to exist, and these 

 forms, so small as to be invisible, might per- 

 haps be the cause of marsh fever ; previous to 

 this men had usually looked upon emanations 

 or injurious gaseous substances as the cause of 

 this fever. Paracelsus had a dim foreshadowing 

 of the truth when he spoke of the " seeds " of 

 disease. The Jesuit Kircher, from observations 

 upon the process of putrefaction and the worms 

 which made their appearance in the course of 

 this process and which he observed with a 

 poor little microscope was the first to develop 

 in a very comprehensive fashion the theory 

 of a " contagium animatum r> (1671). Van 

 Leeuwenhoek, the " father of micrography," 

 was, however, the first really to discover the 

 ' ' world of the infinitely little. " He worked dur- 

 ing the last quarter of the iyth century, with 

 the help of a good microscope that he himself 

 constructed, and studied the organisms found 

 in infusions, putrefying fluids, pus and other 

 substances. Among the organisms that he ob- 

 served and noted were those we now know as 

 bacteria, then perceived for the first time. 



