LIEBIG'S OPPOSITION. 21 



EFFECTS OF SCHWABS DISCOVERIES. 

 These brilliant discoveries very soon attracted general at- 

 tention to the subject from the scientific world, and as iden- 

 tical theories, as we have shown, had long been held as to the 

 modes of propagation and action of contagious diseases, and 

 of fermentation and putrefaction, the theory of a contagiurn 

 vivum again came to -the front, and was urged by some of the 

 strongest minds of the time. The new theory, however, was 

 destined to fight its way inch by inch. Every new fact that 

 was put forth had to pass the most rigid criticism that the 

 opponents of the theory could bring to bear upon it ; and for 

 a time it seemed as if it would be crushed out of existence 

 notwithstanding its apparent demonstration. 



LIEBIG'S OPPOSITION. 



The strongest opponent of the vital theory, as it seems to 

 me, was the then comparatively young Professor of Chemistry 

 at Giessen, Germany, Justus Liebig. Liebig' s view of fer- 

 mentation is practically the same as that enunciated by Willis 

 in 1659, and maintained by others in the succeeding years ; 

 but it is in Professor Liebig's writings that the view reached 

 its highest stage of development and can be best studied. It 

 merits the closest scrutiny, for it has been the principal oppo- 

 nent with which the germ theory has had to contend. If we 

 follow the contests between the chemists on the one side and 

 the vitalists on the other, up to the present time, and analyze 

 the arguments adduced by the chemists, we will find that the 

 very few new facts which they have brought forward have all 

 been based on the plan of Liebig's arguments. There has 

 been nothing essentially new, nor has his argument been 

 strengthened. In the years 1840-42, in response Jx) an invi- 

 tation of the British Association for the Advancement of Sci- 

 ence, Professor Liebig wrote a series of papers upon animal, 



