lO INTRODUCTION 



in which Cagniard-Latour and Schwann established the relation 

 of living yeast to alcoholic fermentation, Donne described vibri- 

 ones (bacteria) in syphilitic ulcers, and Audouin anaplified the 

 discovery of Bassis that muscardine, a disease of the silkworm, 

 was caused by a mold {Botrytis bassiana) which was transmitted 

 from the sick to the healthy worms by contact or by air currents. 

 These discoveries furnished a great impulse to further in- 

 vestigation. 



Henle (1840) reviewed the evidence then at hand and 

 concluded in a very logical way that the causes of contagious dis- 

 eases were to be sought for among the minute living micro-organ- 

 isms. He recognized that no human disease had yet been shown 

 to be caused by a micro-organism and he formulated the require- 

 ments to be fulfilled in order to prove such a relation, namely, 

 that the microbe must be constantly present^ in the disease, 

 must be isolated from the infectious material, and must then 

 alone be capable of producing the disease. 



During the next twenty years, the attempts to discover the 

 cause of an infectious disease and to satisfy the postulates of 

 Henle were successful in several diseases due to molds, Favus 

 (Achorion Schoenleinii) 1839, similar skin diseases known as 

 trichophytosis and pityriasis and especially thrush, shown to be 

 caused by Oidium albicans by Robin in 1847; but in all the more 

 important diseases only failure resulted. The reawakened interest 

 in contagium vivum therefore again gradually faded away. 



During this time Pollender and Davaine and Rayer (1850) 

 had discovered the minute rods in the blood of animals sick with 

 anthrax, and in 1863 Davaine had proved the almost constant 

 presence of these rods in the disease and the possibility of trans- 

 mission by inoculation from one animal to another. 



Pasteur from 1865 to 1868 investigated the fatal disease of 

 silk-worms known as pebrine, discovered the microsporidium 

 (Nosema bombycis) which occurs in the sick worms and in the 

 eggs, and devised a successful method of eradicating the disease. 



In 1870-71 the presence of bacteria in wounds and in the 



