Highlights in the History of Microbiology 37 



miseries, we can note that the ancient Greeks suggested worms, 

 too small to be seen, as the explanation of disease. Marcus Varro, 

 in about 100 B.C., expressed the idea that invisible animals are 

 carried through the air and enter the body by way of the nose 

 and mouth. The Italian physician, Hieronymus Fracastorius ( 1483- 

 1553 ) , in 1546 postulated the theory of contagion, but since he had 

 not actually seen the inciting agents, his thoughts represented pure 



Fig. 12. Robert Koch (1843-1910). {By permission from Intro- 

 duction to the Bacteria, by C. E. Cliftoti. Copyright, 1950. McGraw- 

 Hill Book Company, Inc.) 



speculation. Some two hundred years later (1762) an Austrian 

 physician, Marcus von Plenciz (1705-1786), put forth a new con- 

 cept that not only were diseases caused by microscopic organisms, 

 but each disease was caused by a specific germ capable of being 

 transmitted to other individuals via the air. 



Glossing over these early suggestions, we come to the year 

 1840 when Jacob Henle (1809-1885), a German pathologist, laid 

 down the principles for our present germ theory of disease which 

 led directly to the fundamental work of Robert Koch (1843-1910). 



