22 BACTERIOLOGY. 



wide areas the incubation, course of, and resulting 

 immunity in recovery from infectious diseases all 

 pointed to the probable cause being a living organism. 



Amoug other distinguished men of the day whose 

 observations exerted a most powerful influence upon 

 the doctrine of infection may be mentioned Henle. 

 His writings (Pathological Investigations, 1840, and 

 Text-book of Rational Pathology, 1853), in which he 

 described the relation of micro-organisms to infectious 

 diseases, and defined the character and action of bac- 

 teria upon certain phases and symptoms of these affec- 

 tions, are remarkable for their clearness and precision. 



But, meanwhile, the question which most interested 

 these investigators into the cause of infectious diseases 

 was, Whence are these micro-organisms derived which 

 were supposed to produce them ? Were they the result 

 of spontaneous generation due to vegetative changes in 

 the substances in which the organisms were found, or 

 were they reproduced from similar pre-existing organ- 

 ismsthe so-called vitalistic theory ? This question is 

 intimately connected with the investigations into the 

 origin and nature of fermentation and putrefaction. 



Among those who advocated the theory of spon- 

 taneous generation was Neidham, who, in 1749, at- 

 tempted to prove by experiment the truth of his opin- 

 ions. He placed a grain of barley in a watch-glass 

 containing water, covered it carefully, and allowed it 

 to germinate. On later examination he found bacteria 

 present, which he maintained were the result of changes 

 in the grain itself due to its germination. 



In 1769, Spallanzani showed by another experiment 

 that the theory of spontaneous generation was incor- 

 rect. He demonstrated that if putrescible infusions 



