NEW CONCEPTIONS IN SCIENCE 



produced exactly the same fermentive action as the 

 yeast-cells themselves. Obviously fermentation is 

 due to the presence in the yeast-plants of a chemical 

 substance which may be expressed out of them. 

 Pasteur's mysterious "vital action," then, seemed 

 a myth. 



This decisive experiment derived especial im- 

 portance from the fact that it came as a sort of 

 climax to a long series of researches which had 

 already disclosed the far-reaching role of fermen- 

 tive action. Long before the days of Pasteur two 

 French investigators had succeeded in isolating 

 from germinating grain a substance that seemed 

 to possess almost unlimited capacity for splitting 

 up starch into simpler compounds. Later it was 

 found that the saliva of the mouth contains a 

 substance possessing the same power. Its dis- 

 coverer, not knowing much about it, named it 

 ptyalin. 



Then came the discovery, in the stomach, of the 

 substance familiar now to every one under the name 

 of pepsin. It acts especially on the proteids, the 

 meat- and egg-like foods. In the bile secreted by 

 the liver was found another, whose work it is to 

 make an emulsion of the fat foods, so that they 

 may be taken up by the blood ; the pancreas manu- 

 factures another, which completes in the intestines 

 the work begun by the ptyalin of the mouth ; and 



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