ALCOHOLIC FERMENTS. 155 



temperature approaching their maximum temperature, they 

 became affected in such a manner that they lost their power 

 of forming spores, and the same applies also to the innumer- 

 able generations gradually formed in new cultures at the 

 optimum temperature. Yet the cells had a vigorous appearance 

 and were further cultivated under very varied conditions. 



Similar changes were also brought about by cultivation 

 on a solid nutritive medium. These newly-formed varieties, 

 as Hansen provisionally calls them, have not only lost their 

 power of spore-formation, but at the same time also their 

 property of forming films. 



- These investigations also have a practical bearing on the 

 breiuing industry, although in a direction different from that 

 of Hansen's earlier researches. The Carlsberg bottom-yeast, 

 No. 2, well-known to the brewing world, is one of the species 

 which loses the property of spore-formation when it is subjected 

 to the above-mentioned treatment. In the case of this yeast, 

 it has been proved by numerous experiments that, simul- 

 taneously with the change mentioned, the plasma of the cells 

 also undergoes transformation in other directions. The 

 newly-formed growth gives a more feeble fermentation, the 

 higher percentages of alcohol being produced more slowly than 

 usual ; in short, after the yeast has been treated as described, 

 it works in a different manner than before such treatment. 



No objection can be raised to the view that we are here 

 possibly dealing with the formation of new species. We 

 know in fact that the species are not fixed and unchangeable, 

 as was generally assumed in Linnets time, but that the 

 characters of a species are only constant under certain con- 

 ditions. The complete elucidation of these important and 

 intricate problems can, however, only be effected by a series 

 of experiments carried on through a long period of time and 

 varied in different directions. 



In order to guard against any misunderstanding, it may 

 not be superfluous to remind the reader that these remarkable 

 changes are only brought about by a long-continued and 



