INTRODUCTION 21 



yet it was found that boiled decoctions would not always remain 

 free from microorganisms. The theory of spontaneous generation 

 of these bacteria was opposed by some and supported vigorously by 

 others of the best scientists of the time. Experiments were care- 

 fully planned and a great variety of materials used, paving the way 

 for the development later of the laboratory technic of the bacteriol- 

 ogist. The sterilizing action of heat, the antiseptic action of 

 certain chemicals, and the value of the cotton plug as a bacterial 

 filter were demonstrated. The theory of spontaneous generation 

 as a topic of contention practically disappeared about 1860. 

 This was largely due to the efforts of Pasteur, who, by a long 

 series of ingenious experiments, overthrew the last defense of the 

 supporters of the theory. The dictum, omne viuum ex vivo (all 

 life from life), is universally accepted at the present time, and the 

 controversy has little but historic interest. 



Relationship of Microorganisms to Fermentation and Decay. 

 As has been previously noted, some of the early philosophers 

 hazarded the opinion that decay might be caused by invisible 

 living beings of some kind. The causal relationship of micro- 

 organisms to decay and particularly to fermentation was first 

 definitely established by the work of Louis Pasteur (1822-1895). 

 He found the production of alcohol and carbon dioxid from sugar 

 was due to a yeast, that milk soured because of the activity of 

 bacteria, and that many of the familiar changes in organic sub- 

 stances were accomplished by microorganisms. His conclusions 

 were strenuously opposed and ridiculed by the great German 

 chemist, Liebig. Doubtless the necessity for meeting the attacks 

 of the latter and of establishing his points beyond possibility 

 of refutation led him to devise and develop many of the laboratory 

 methods in common use at the present time. As a result of 

 Pasteur's work the fundamental importance of bacteria in the trans- 

 formation of nitrogen and carbon compounds in nature, the 

 disposal of waste, the purification of water, the enriching of the 

 soil, and many of the changes in the manufacture of foods have 

 been established. 



Relationship of Microorganisms to Disease. The probable 

 causal relationship of microorganisms of some kind to disease 

 was argued as long ago as 1762 by Blencig, of Vienna. His 



