84 MICEOBES, FEEMENTS, AND MOULDS. 



The dragon-trees (Draccena terminalia and D. 

 Australis) also possess a feculent root, from wliicli a 

 fermented liquor is extracted in the same manner by 

 the Sandwich Islanders. 



VI. The 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. 



