THEOEIES AS TO THE ORIGIN OF LIFE. 79 



If we make a thick syrup of cane-sugar, and 

 strew a few particles of this yeast upon it, they 

 will begin to grow and propagate, will cause 

 minute bubbles of gas to rise, and the whole 

 syrup gradually to ferment. . . . In the juice of 

 ripe grapes, it has a more favourable medium 

 still. If we filter this juice, we obtain a clear, 

 transparent liquid. Within half an hour this 

 liquid begins to grow first cloudy, and after- 

 wards thick, to give up bubbles of gas, or to 

 ferment, and in three hours a greyish yellow 

 layer of yeast has been already collected on its 

 surface. In the heat of the fermentation the 

 plants are produced by millions a single cubic 

 inch of such yeast, free from adhering water, 

 containing eleven hundred and fifty-two mil- 

 lions of the minute organisms. . . . The cells, 

 or globules, vary in size from y-gVcr to ^Vir of 

 an inch. . . . Whence come the seeds of this 

 yeast-plant, which propagates itself with such 

 wonderful rapidity ? Do they exist already in 

 the juice of the living grape ? Do they cling to 

 the exterior of the fruit, or do they float perpe- 

 tually in the air, ready to germinate and mul- 

 tiply wherever they obtain a favourable oppor- 



