6 AGEICULTUEAL AND INDUSTRIAL BACTERIOLOGY 



was evolved, and finally in 1870 the substage condenser 

 developed by Abbe. Microscopes comparable in efficiency 

 to those in use now were unknown before this time. Cohn 

 in 1872 clearly presented the differences between the true 

 bacteria and the protozoa. He placed the bacteria with 

 the plants and worked out a fairly comprehensive and 

 satisfactory classification of genera and species. Since 

 that date advance has been comparatively rapid. 



Controversy over the Theory of Spontaneous Genera- 

 tion. — Some of the earlier observers of bacteria and other 

 microorganisms expressed much curiosity as to their origin. 

 It was observed, for example, that if a decoction of vege- 

 tables or hay was exposed to the air for a time, the liquid 

 soon swarmed with bacteria. Apparently living things ex- 

 isted where there had been no observed living things be- 

 fore. Many investigators arrived at the conclusion that, 

 unlike higher forms of life, bacteria might originate de novo, 

 that is, without preexisting organisms of the same kind. 

 In fact, they concluded that when there existed a right mix- 

 ture of water and dead organic material, the right exposure 

 to air, and the right temperature, there was inherent ability 

 on the part of the organic material to change in part to 

 living cells. This point of view was opposed by other scien- 

 tists, particularly by Pasteur and Tyndall, who contended 

 that microorganisms must always come from preexisting 

 microorganisms of the same kind, and that there is no 

 proof of spontaneous generation as it concerns bacteria was 

 quite definitely demonstrated. As a result of the laboratory 

 studies on this problem the foundation was laid for modern 

 bacteriology, and many of the methods used in the labora- 

 tory to-day were first developed by those who took a lead- 

 ing part in the settlement of this dispute. 



The Controversy over the Germ Theory of Fermenta- 

 tion. — Chemistry as a science is somewhat older than 

 bacteriology. Among the subjects which have interested 



