22 THE GERM THEORY OF DISEASE. 



vegetable and agricultural chemistry and the chemical trans- 

 formations, including the action of the different ferments, 

 yeast, putrefaction, contagion, miasrn, etc., in which he antago- 

 nized the vital theory of each of these with all the vigor of his 

 wonderful intellect, and for the time crushed the rising confi- 

 dence in the new theory. 



The arguments brought forward by Liebig may be summed 

 up as follows : u Fermentation is a result of the catalytic action 

 of a decomposing body in contact with compounds of feeble 

 molecular affinity, which is brought about in accordance with 

 the following law of dynamics: A molecule set in motion by 

 any power can impart its own motion to another molecule 

 with which it may be in contact." Yeast, he argued, is a pro- 

 duct of the decomposition of gluten, and is necessarily a de- 

 composing body, and when added to must or wort, sets up in 

 these bodies a motion of their molecules similar to its own, by 

 which their saccharine elements are converted into the simpler 

 and more stable compounds, carbonic acid and alcohol. 



But the action upon the gluten is to convert it into a body 

 identical with the original yeast. And thus the yeast seemed 

 to grow ; but it is not a growth in the biological sense. This, 

 he contended, is demonstrated by adding yeast to a pure solu- 

 tion of sugar, in which case, although the fermentation pro- 

 ceeds promptly, the quantity of the yeast not only did not 

 increase, but actually diminished, being expended in the act 

 of decomposition. 



Putrefaction, he says, is just the same process, but with a 

 different molecular motion. These molecular motions might 

 reproduce themselves or not, as the substance on which they 

 acted contained the substance from which they were pro- 

 duced or not. Miasms and contagions were considered as 

 being of the same character. 



His idea of a chemical force more powerful than the vital 



