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ment of the germ theory now resolves itself. Starting with 

 Leeuwenhoek's discovery of micro-organisms, Cagniard 

 La Tour and Schwann's discovery that the globules of yeast 

 are living plants capable of indefinite multiplication in 

 suitable media, and Pasteur's demonstration that fermenta- 

 tion in general is necessarily associated with the presence 

 of living organisms, we have opened up a series of most 

 profound inquiries into the relations between chemical force 

 and aflanities in general and that undefined something 

 which may be provisionally called vital force. From 

 speculations as to the influence of vital force on the chemistry 

 of nature in general, concerning which vastly wider views 

 are now presented than were dreamt of in the pre-Pasteurian 

 period, we naturally pass to inquiries as to the influence of 

 chemical conditions upon the special forms and the special 

 attributes of particular forms of organized life. From such 

 inquiries we proceed to inquiries as to the origin and nature 

 of microbes themselves, and the phenomena of their patho- 

 logical relations. 



8. — With the overthrow of Liebig's motion or contact 

 theory of fermentation, and the substitution of Pasteur's 

 demonstrations that fermentation is a vital process, our 

 view of the influence of the unknown force, vitality, in the 

 chemistry of nature, has become so vastly extended that it 

 may almost be said that chemical changes are dependent 

 upon life. Death itself is life. The tendency is to the 

 conclusion that no other foims of force could exert 

 a sustained influence in rearranging the elements of 

 matter. The changes possible in consequence of mere 

 thermal or electrical conditions are so strictly limited that 

 it may be said that without vitality certain forms and com- 

 binations of matter must have been eternal. Chemical 

 afiinity alone must have resulted in absolute stability. 

 Wc may conceive the possibility of heat from an external 

 source breaking up any matter, even living matter; but it 



