264 MAN'S IMPROVEMENT OF HIS ENVIRONMENT 



Place the three Petri dishes in a moderately warm and dark 

 place for three days. Then examine. 



Observations. In which of the three dishes are the most 

 colonies of bacteria and molds? Continue your observations for 

 about one week's time. 



Conclusion. Which of the above methods of dusting a room 

 is the most hygienic and why? (Read Hodge, Nature Study and 

 Life, page 476.) 



Problem 236 : What should I eat for luncheon ? 



Materials. Food tables on pages 204 to 209. 



Method and Observations. Eight boys in a class eat the 

 following lunches : 



A brings from home two ham sandwiches, a sponge cake, and 

 an orange. 



B brings from home two cheese sandwiches and buys a glass of 

 milk and five cents' worth of candy. 



C buys a hot roast beef sandwich, a cup of cocoa, and an 

 apple. 



D buys a dish of ice cream, one piece of sponge cake, and five 

 cents' worth of candy. 



E brings two slices of bread and a square of chocolate and buys 

 a glass of milk. 



F buys a Frankfurter, a roll, a small helping of sauerkraut, 

 and a glass of lemonade. 



G buys a plate of vegetable soup, a slice of bread and butter, 

 a cup of tea with milk and sugar, and a piece of apple pie. 



H buys a helping of beans and a dish of ice cream. 



Using the tables on pages 204-209, work out the proportion of 

 carbohydrate, fat, and protein contained in each. Add up the 

 total number of Calories in each. Use any standard you wish, 

 Atwater, Chittenden, or Voit. 



In like manner add your own luncheon to the list. 



Conclusion. Which do you think the best balanced ? Which 

 the most poorly balanced? Which the cheapest (most nutri- 

 ment for the least money) ? Which the best for a spring or a fall 

 luncheon ? 



