Chemical Changes in Animal Organism. 289 



Cagniard-Latour, Theodor Schwann, and Kiitzing, pub- 

 lished memoirs in which they brought forward certain 

 evidence indicating the fact that yeast was a living 

 organism. A very important observation is due to 

 Schwann, who showed that if matter which normally 

 undergoes putrefaction on exposure to air is treated in 

 such a way that all living organisms are destroyed, it 

 will remain intact, and can be preserved for an indefinite 

 period without undergoing putrefactive changes. Thus, 

 if animal or vegetable matter is heated in a vessel, and 

 the air which subsequently comes into contact with it is 

 filtered or passed through concentrated sulphuric acid, it 

 will not undergo putrefaction. The conception appeared 

 to be established that both fermentation and putrefaction 

 were due to the agency of living organisms. The con- 

 clusions of Cagniard-Latour and of Klitzing were based 

 chiefly on the microscopical evidence. Other investigators, 

 who worked before the three above-mentioned, had also 

 obtained indications as to the nature of fermentative and 

 putrefactive processes, but the evidence obtained by them 

 was scarcely so definite. Nevertheless, the views as to the 

 vital agency were for a long time controverted, especially 

 by Liebig and Berzelius, who at the time were regarded 

 as the leaders of chemical thought, and it was not till 

 about 1857, when Pasteur published his classical re- 

 searches, tli at the correct views as to the nature of yeast 

 and other micro-organisms commenced to be almost uni- 

 versally accepted. To Pasteur is due the greater part of 

 the modern technique for the culture of the pure organisms, 

 of which a great variety exists always in the air, and for 

 the methods of investigation of the chemical changes pro- 

 duced by them. To-day there is practically no question 

 of the fact that fermentation, putrefaction, and certain 

 pathological conditions in both animals and plants are due 



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