Reproduction of Vegetal Cells. 230 



sprouting. " He draws the inference that the adherent particles are the 

 ferment. * ' The ferment of the grape clings like a parasite to the sur- 

 face of the grape. " 



But how about beer? If the beer-wort is exposed to the air it 

 ' ' sooner or later ferments; but the chances are that the produce of that 

 fermentation instead of being agreeable would be disgusting to the 

 taste. By a rare accident we might get true alcoholic fermentation, but 

 the odds against obtaining it would be enormous. Pure air acting upon 

 a lifeless liquid will never provoke fermentation, but our ordinary air 

 is the vehicle of numberless germs which act as ferments; when they fall 

 into appropriate infusions, some of them produce acidity, some putre- 

 faction. The germs of our yeast plant are also in the air but so spar- 

 ingly distributed that an infusion like beer-wort exposed to the air is al- 

 most sure to be taken possession of by foreign organisms. In fact, the 

 maladies of beer are wholly due to the admixture of these objectionable 

 ferments whose forms and modes of nutrition differ materially from 

 those of the true leaven. " 



Thus we understand Prof. Tyndall that the germs of the yeast plant 

 are scarce in the air. Yet they are so abundant on the skins and stems 

 of grapes that they invariably set up the true alcoholic fermentation. 

 They evidently, then, must be far too numerous on the skins and stems 

 of grapes to have been derived merely from the air ; for we are to con- 

 clude that they are on all grapes ; since fermentation will take place 

 in all. If the supply comes to the grape from the air why not also to 

 the beer-wort? Has the grape some peculiar attraction for these para- 

 sites? Are these germs just as thick on every other object as upon the 

 grapes? If not, why not? It is decidedly improbable that they are on 

 all objects in such abundance as they appear to be on the grapes. 

 There are many localities in which a vineyard, an acre in extent, may 

 be surrounded by fifty square miles destitute of vines. Must we sup- 

 pose all such districts to be thickly sowed year after year with yeast 

 germs which never sprout but are nipped by the frosts of every autumn? 

 Whence comes this annual supply in such enormous and wasteful abun- 

 dance? Bacteria germs we might reasonably expect to be tolerably 

 plentiful, for they would become exposed to the winds on the drying 

 margins ol every ditch and pond during the summer months. But the 

 yeast plant is far more dainty. It does not live in ponds and ditches 

 nor flourish in filth. In clear water it lives on its own tissues till it is 

 self consumed. It must have the rich carbonaceous compound to draw 

 its sustenance from. Almost the sole supply of such compounds and 

 infusions as the yeast plant affects are those formed by human agency, 

 in beer and wine vats. These are tolerably plenty in Europe, but they 

 are scarce in the western states and territories of America. But every- 



