PROBLEM 171 195 



the laboratory work can be transferred to the hilx)ratory of home economics or to 

 the home. 



Problem 170: How to deternvine the nutritive value of fond . 



Materials. — Set of government charts on food values. Tables 

 on pages 276, 278, 279, Civic Biology. 



NOTE. — Food has two possible vahaes : it may be oxidizofl to release enercy or 

 it may help build tissue. The burning value of foods may ]>c measured by heat 

 units called Calories (a Calorie is the amount of heat needed to raise the tempera- 

 ture of a kilogram of water through one degree centigrade). Remember food is 

 composed of nutrients, water, and refuse. Therefore not all food taken into the 

 body is made use of. 



Observations. — In the chart on page 27G, Civic Biologij, deter- 

 mine the actual percentage of nutrients in beef, potatoes, oysters, 

 and corn meal. Do all foods have equal nutritive value? 



From the government charts make a table in which you will place : 



(a) Ten foods rich in protein (15 per cent or more). 



(6) Ten foods rich in carbohydrates (50 per cent). 



(c) Ten foods rich in fat (50 per cent or more). 



(d) Ten foods having a high fuel value (1500 Calories or more 

 per pound). 



(e) Ten food substances that are over 50 per cent water. IIow 

 would water affect the cost of food, providing you had to pay for 

 the water? 



(/) Five foods rich in mineral salts. 



Conclusion. — In your opinion which of the foods shown are 

 the best tissue-building foods ? The best energy-producing foods ? 

 Explain. Remember that hving matter is made uj) of carbon, 

 oxygen, hydrogen, nitrogen, sulphur, and a minute amount of 

 mineral salts. 



JProblem 171: The use of the bortih calorimeter. (Optional.) 



The bomb calorimeter may be demonstrated by the instructor and its mechan- 

 ism explained. Roys should be urged to try to experiment at home with homemade 

 apparatus. An interesting series of home experiments on the burning value of 

 different food sul)stances worked out first hand will do much toward getting indi- 

 vidual interest in the topic. Cirls should ai)proach this entire subject from the side 

 of household economics. Much work can be done in household economics that will 

 be scientifically explained in the biological laboratory, the two subject.s giving und 

 taking much from common ground. 



