356 Our Surroundings 



It has been observed that people who live on a restricted diet of 

 only a small variety of foods do not always enjoy the best 

 of health, even though they have a sufficient quantity of all 

 the five nutrients protein, fats, carbohydrates, water, and min- 

 eral matter. This has led to the theory that there are certain 

 substances, called vitamins, which are required by the body, al- 

 though their nature is not yet understood. They occur in many 

 food substances, including milk, eggs, fresh vegetables, and fruits. 

 It is claimed that vitamins are sometimes lost to us because of the 

 way we prepare foods, as by removing the outer covering of 

 wheat in making flour, or by discarding the skins of potatoes. 

 The absence of vitamins is supposed to cause scurvy which was 

 formerly the bane of sailors who went on long cruises and were 

 obliged to live on a meager variety of diet. In order to supply 

 vitamins, there should always be a moderate amount of uncooked 

 foods in the diet, such as raw fruits, tomatoes, and green vege- 

 tables. The juice of oranges is recommended by physicians for 

 infants, to supply vitamins in their diet. Sunlight contains a 

 vitamin which enters any body exposed to it. 



Experiments to Show the Characteristics of Some Nu- 

 trients and Their Presence in Commom Foods. Certain chem- 

 icals produce characteristic changes in food substances, and conse- 

 quently may be used to show the presence of these substances in 

 different kinds of food. For example, iodine solution is a test 

 for starch. If starch is present in a food tested with iodine 

 solution, a blue color will be produced. Fehling's solution is a 

 test for grape sugar. If grape sugar is present in a food Fehling's 

 solution will produce a color varying from yellow to brick-red 

 according to the amount of sugar present. Nitric acid is a test 

 for protein. If protein is present, the acid will produce a yellow 

 color which will become orange if drops of ammonia are added. 



In making tests for fat, for water, and for mineral matter, 

 it should be remembered that white paper rubbed with a food con- 

 taining fat will appear translucent when held before the light; 

 that if food containing water is heated, the water will evaporate 

 and condense on a piece of cold glass held over it ; and that sub- 

 stances containing minerals leave ashes when burned. 



