32 



(e) Scrape a bit of potato, thin it with water, and put 

 a drop on the microscope slide. State clearly what you 

 see under the microscope and make a rough drawing. 



(/) In a similar manner examine a bit of cooked potato. 



The starch found in uncooked vegetables, cereals, etc., 

 is in the form of small grains which have a hard outer 

 shell. The digestive juices of the body cannot readily 

 penetrate this hard shell, and hence raw starch is indi- 

 gestible. Heat or cooking softens the shells, swells the 

 starch, and causes the grains to burst; hence the grains 

 of cooked starch are in a condition in which the digestive 

 fluids can reach them and act upon them. For this reason 

 vegetables, fruits, cereals, and all starchy foods are more 

 digestible when cooked than when raw. 



EXPERIMENT 21. THE PRESENCE OF FATS IN SOME 

 COMMON FOODS 



(a) Scatter a spoonful of corn meal lightly on a thin 

 sheet of clean paper, and lay the paper on a tin plate. 

 Then put the plate in a drying oven for a few minutes, 

 or if that is not possible, put it on a hot radiator. Is there 

 any indication that the corn meal contains oil or fat ? 



(b) Shell a peanut and cut it into small bits ; test as 

 before. Is the result the same ? 



(c) Shave a piece of cheese into fine bits and place 

 these in a test tube. Add sufficient ether to cover the 

 cheese, then cork the tube and allow it to stand for thirty 

 minutes. At the expiration of that time, strain the result- 

 ing solution into a shallow dish and allow the solution to 

 stand until the ether has evaporated. What remains in 

 the dish ? 



