84 MICROBES, FERMENTS, AND MOULDS. 
The dragon-trees (Dracwna terminalis and D. 
Australis) also possess a feculent root, from which a 
fermented liquor is extracted in the same manner by 
the Sandwich Islanders, 
VI. Tue LEAVEN oF BREAD. 
Bread is leavened in order to make it porous and 
more digestible. According to Engel, the microbe of 
baker’s yeast is Sacch. minor, resembling that of beer- 
yeast, only more minute. Most of the yeasts which 
we have examined contain a great variety of microbes. 
However this may be, the fermentation of bread, like 
other fermentations, sets free carbonic acid gas, and 
this raises the dough and makes it light. 
