70 SELECTION AND PREPARATION OF FOODS 



When the stones were sufficiently hot, the fire was 

 brushed off, and the food, whether dough, fish, or fowl, 

 was spread upon them. Ultimately, quite elaborate bak- 



FIG. 50. Cells of a raw potato, with starch grains in natural condition. 



ing structures were developed, of which the brick oven 

 used by our grandmothers is an example. 



Boiling. With the invention of pottery and later 

 of metal vessels which would hold liquids without 



Cellulose 

 envelope 

 -Baked 

 starch 



FIG. 51. Baked potato, showing masses of cooked starch within envelopes of 

 cellulose. (Bulletin of Agricultural Department.) 



cracking, cooking by boiling was naturally added 

 to roasting and baking. Frying, which is such a com- 



