FOODS AND THE THEORY OF DIGESTION 137 



the liquid is now boiled, the color deepens and this may be contrasted 

 with the blue color below. Apply this test to the sugar in raisins and 

 in honey. 



Fat. Fat is recognized by its effect on paper, making a greasy stain 

 which does not disappear on heating and which renders the paper trans- 

 lucent. Try butter, lard, or olive oil. Also show the presence of fat in 

 peanuts by crushing them in a mortar and rubbing the powder on thin 

 paper. If the substance to be tested contains but little fat, this may be 

 dissolved out with ether. If a drop of ether containing the fat is placed 

 on paper, it evaporates, leaving the fat, which then forms the stain. 



To show the Effect of Alcohol upon Proteid. Place some of the 

 white of a raw egg in a glass vessel and cover it with a small amount of 

 alcohol. As the albumin (proteid) hardens, or coagulates, observe that 

 the quantity of clear liquid increases. This is due to the withdrawal 

 of water from the albumin by the alcohol. Since the tissues are made 

 up chiefly of proteids, a piece of muscle or of liver may be used in the 

 experiment, instead of the egg, with similar results. 



To illustrate the Digestive Process. To a tumbler two thirds full 

 of water add a little salt. Stir and observe that the salt is dissolved. 

 Taste the solution to see that the salt has not been changed chemically. 

 Now add a little powdered limestone to the water and stir as before. 

 Observe that the limestone does not dissolve. Then add some hydro- 

 chloric acid and observe the result. State the part played by the acid 

 and by the water in dissolving the limestone. Apply to the digestion 

 of the different classes of foods. 



