HISTORICAL INTRODUCTION. 457 



yeast reproduction and alcoholic fermentation seem to be two 

 distinct phenomena. As far back as 1839, J. LIEBIG (I.) classed 

 fermentation and putrefaction as the results of the transmission of 

 chemical motion, proceeding from a proteid (" ferment ") substance 

 in a state of incipient decomposition. At a later date (1870) 

 this worker (II.) expressed the opinion that this chemical ferment 

 was a nitrogenous and sulphurous body present in the yeast cell 

 in a state of decomposition and transformation ; and that the 

 sugar of the fermenting liquid combined with the proteid sub- 

 stances in yeast to form a solid protein saccharate, alcohol being 

 then separated in consequence of the rearrangement of one or 

 more constituents of the ferment. A similar view was strongly 

 supported by HOPPE-SEYLER (VI.), who wrote : " Lower organisms 

 are undoubtedly producers and carriers of ferments just the same 

 as higher ones. In my opinion, the possibility of the production 

 of an alcoholic ferment by germinating yeast is established in 

 principle by the separation of invertase from the yeast cell." 



Although the existence of a fermentative enzyme was assumed 

 by celebrated scientists, and the possibility of the production of 

 such a substance by budding beer yeast was brought within the 

 bounds of probability, for example, by the discovery of FIECHTER 

 (I.) that hydrocyanic acid destroys the vitality and development 

 of yeast completely, though not necessarily its action as a ferment, 

 an important difference still existed between the enzymes already 

 known and that concerned in alcoholic fermentation. The 

 former were able to perform their functions even when separated 

 from the living cell, whereas the hypothetical yeast enzyme 

 could not at first be isolated from the living cell. The question 

 arose, given such an enzyme in beer yeast, why cannot it be 

 isolated, and since experience teaches that enzymes act only when 

 in a dissolved condition, why is the yeast cell alone able to set up 

 the fermentative action ? This question became particularly 

 important when Berthelot and Liebig succeeded in isolating 

 invertase from the yeast cell. 



All the attempts made by workers at different times to separate 

 an alcoholic ferment from the yeast cell proved futile. Thus, the 

 experiments of BERTHELOT (V.), for recovering the enzyme from 

 yeast by maceration, failed. MITSCHERLICH (IV.), HELMHOLTZ 

 (I.), DUMAS (V.) and others filtered the yeast liquid, or tried to 

 separate the yeast from the dissolved constituents by diffusion 

 through a fine membrane, but in none of these cases was any fer- 

 mentation set up so long as reinfection with yeast cells was 

 carefully precluded. Even wort tha.t is in full fermentation soon 

 ceases to ferment when the yeast cells are removed by filtration 

 and the access of new yeast cells is prevented. This experiment 

 was recently repeated by WROBLEWSKI (V.), who employed 

 sandstone as the filtering medium. A different result was 

 obtained by COLIN (I.) and afterwards by FLECK (II.), but their 





