vigorous fermentation — production of alcohol and car- 

 bon dioxide — to occur, and the cells rapidly multiplied in 

 number during the process. Pasteur therefore concluded 

 that fermentation was due solely to the metabolic acti- 

 vities of enormous numbers of microscopic organisms — 

 the bacteria. The alcohol and carbon dioxide which fer- 

 mented grape juice contained were the waste products of 

 the wine-forming bacteria, while the grape sugars were 

 their food. 



Once Pasteur had realized that bacteria could produce 

 chemical changes as striking as fermentation, and that 

 bacteria occurred everywhere — in soil, water, and air — 

 he sought to find other effects which might be ascribed 

 to bacterial action. He showed, for example, that the 

 decaying of a beef broth after exposure to the air, was 

 due to bacteria entering the liquid and multiplying in it, 

 with the formation of noxious substances: a broth, thor- 

 oughly sterilized first by boiling in a closed vessel, re- 

 mained fresh indefinitely, since no bacteria were present 

 in it: (heating killed any which were in it to begin with). 

 This observation disproved the theory of spontaneous origi- 

 nation of microorganisms accepted by some biologists at 

 the time. 



Pasteur now started to examine fluids taken from dis- 

 eased animals and humans for possible bacteria which 

 might, he thought, be the cause of various diseases, and 

 in the cases of anthrax (a serious disease of sheep), chicken 

 cholera, and a disease of silkworms he was able to see 

 bacteria of different kinds in the microscope. (However, 

 he could not observe any bacteria in fluid from a human 

 affected with rabies — this disease is caused by a virus 

 too small to be seen with the microscope: nevertheless 

 Pasteur developed a successful treatment for the otherwise 



57 



