A STUDY OF FOODS AND DIETARY 351 



Warm the mixture gently. What color is produced? Now add 

 ammonia solution until the mixture smells of the ammonia. What 

 has happened to the color just observed? Care should be used to 

 prevent any nitric acid from getting on the skin for it produces a 

 disagreeable stain. Why? 



389. The Protein Foods Absolutely Necessary. While 

 the protein foods yield energy equal in amounts to equal 

 weights of carbohydrates, their chief value to the body lie^s in 

 the fact that they alone contain nitrogen. Proteins must be 

 found in every diet. The body may obtain energy quite as 

 well from fat and carbohydrate as from protein, but neither 

 fats nor carbohydrates can furnish the body with the nitrogen 

 which it needs. Moreover, the protein foods, as a rule, are 

 higher in price than either the carbohydrates or the fats. It 

 would be folly therefore to consume protein foods for the 

 sole purpose of producing energy for the body when this energy 

 can be obtained more cheaply from carbohydrates and fats. 

 Moreover, the waste products from protein are much harder 

 to get rid of than the waste products from carbohydrates and 

 fats. However, enough protein must be supplied the body 

 at all times to keep the body in repair. 



390. How Much Protein? This is a matter which has 

 caused a great deal of discussion. But authorities are now 

 agreed that the body should be supplied with from 3 to 5.3 

 oz. of protein per day. Dr. Atwater gave the following as the 

 protein requirement of persons engaged in different occupations : 



Man with hard muscular work 5.3 oz. per day 



Man with moderately active muscular work 4.4 oz. per day 



Man at sedentary or woman with moderately ac- 

 tive work * 3.5 oz. per day 



Man without muscular exercise or woman at light to 



moderate work 3.17 oz. per day 



Exercise 79. Weighing the Amount of Protein Needed by the 

 Body for a Day 



Weigh a dozen eggs and calculate the average weight of one egg. 

 By the use of Table XIV on page 353 or Fig. 247 which gives the 

 oercentage of protein in whole eggs, calculate the weight of egg 



