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starch, is made into a paste with water, and immedi- 

 ately and gradually heated to about 44O, it increases 

 in weight, and is found entirely altered in its proper- 

 ties ; it has lost its solubility in water, and its power 

 of being converted into sugar. In this state it is un- 

 leavened bread. 



When the flour of corn or the starch of potatoes* 

 mixed with boiled potatoes, is made into a paste with 

 water, kept warm, and suffered to remain 30 or 40 

 hours, it ferments, carbonic acid gas is disengaged 

 from it, and it becomes filled with globules of elastic 

 fluid. In this state it is raised dough, and affords by 

 baking, leavened bread ; but this bread is sour and 

 disagreeable to the taste ; and leavened bread for use 

 is made by mixing a little dough, that has fermentec}, 

 with new dough, and kneading them together, or by 

 kneading the bread with a small quantity of yeast. 



In the formation of wheaten bread more than 1-4 

 of the elements of water combine with the flour ; 

 more water is consolidated in the formation of bread 

 from barley, and still more in that from oats ; but 

 the .gluten in wheat, being in much larger quantity 

 than in other grain, seems to form a combination with 

 the starch and water, which renders wheaten bread 

 more digestible than the other species of bread. 



The arrangement of many of the vegetable prin- 

 ciples in the different parts of plants has been inciden- 

 tally mentioned in this Lecture ; but a more particular 

 statement is required to afford just views of the rela- 

 tion between their organization and chemical constitu- 

 tion, which is an object of great importance. The 



