THEORIES OF FERMENTATION. 239 



dioxide is evolved from the tube. It is only after some time, 

 when the paper softens and allows the yeast globules to pass 

 through, that the fermentation process begins to take place 

 on the surface of the paper. He concludes that " fermentation 

 only takes place at the surface of the globules." He also 

 published beautiful drawings of yeast, showing their methods 

 of growth and propagation, and described the contents o the 

 cell after staining with iodine. 



All these observations did not suffice to establish the new 

 theory. The great authority of the chemist, which still 

 prevailed, required an equal authority in the region of biology 

 to take up every point of the discussion, and by convincing 

 experiments along the whole line, to compel attention ; lacking 

 such an authority, the earlier disputants were unable to win 

 the victory. 



This great work was carried out by Pasteur with the same 

 conclusive results as in the case of generation. The investi- 

 gations begun by Pasteur did not consist, like those of the 

 earlier experimenters, of short, isolated pieces of work, but 

 ranged over a series of years from 1857 onwards, and were 

 published in a number of memoirs. In this short review it 

 is impossible to do more than indicate a few isolated and 

 especially important experiments taken from the series, which 

 ranges over the whole field of fermentation. 



At an early stage he made the important observation that 

 the amount of sugar dissolved during fermentation is greater 

 than that corresponding to the carbon dioxide and alcohol 

 produced. The remainder of the sugar that disappears is 

 utilised by the yeast during fermentation, partly for its pro- 

 pagation a circumstance which cannot be reconciled with 

 Liebig's view, who demanded as a condition of fermentation 

 that yeast should be in a state of decomposition. Shortly 

 after, Pasteur proved that during fermentation yeast not only 

 produces alcohol and carbon dioxide, but simultaneously 

 succinic acid and glycerine, the latter derived from a further 

 part of the disappearing sugar. He also showed that by the 

 addition of ammonium tartrate to the fermenting liquid yeast 

 can be brought to more rapid development, and the liquid can 

 be more highly fermented than usual, proving that this salt 



