12 MANUAL OF BACTERIOLOGY. 



chiefly with respect to infusoria and other relatively large forms. 

 In 1840 Henle described the part played by micrcorganisms 

 in producing disease in terms surprisingly in accord with views 

 held at the present time. His deductions were based almost 

 entirely on knowledge of the general nature, spread and course 

 of infections. So, too, Villemin anticipated the discovery of the 

 bacillus of tuberculosis, for he transmitted the disease to animals, 

 by inoculating them with material from cases of tuberculosis 

 in man. 



The key to exact knowledge of the microorganisms of disease 

 was finally discovered in the study of fermentation. No better 

 illustration could be found of the possible value to mankind which 

 may lie in any addition whatever to the common stock of 

 knowledge. The study of bottles of bad-smelUng broth would 

 have seemed, fifty years ago, a most unpromising beginning for 

 the discovery of the causes of cholera, plague, and the like, or 

 for an antitoxin for diphtheria. 



Studies on Fermentation and Spontaneous Generation. — 

 Two observers (Schwann, Cagniard-Latour, 1837) almost 

 simultaneously stated the proposition that yeast cells were 

 living organisms, and that the fermentation of solutions of sugar 

 was due to their growth. From this time ensued a controversy 

 which lasted more than thirty years. The agency ascribed to 

 yeasts was energetically denied by many, prominent among them 

 Liebig; while it was sustained with vigor by others. The 

 latter extended the original conception to include other sorts of 

 fermentation and the putrefaction of albuminous material. 

 Different kinds of fermentation, with different products, such 

 as acetic acid and butyric acid, were ascribed to the growth 

 of different kinds of microbes. 



These microbes were found to be fungi of various sorts, and 

 chiefly one or another variety of bacteria. The most celebrated 

 among the students of fermentation was Pasteur, the simplicity 



