4 The Composition and Food Value of Bread. 



from at any rate the grosser impurities with which foreign 

 wheat is often contaminated. The matter is obviously one 

 of great complexity, and can only be solved by appeal to 

 experimental results. 



Before turning to experimental results, however, it may 

 be well, briefly, to discuss the food requirements of an average 

 healthy man. In order that a man may be maintained in 

 a state of health, it is necessary that his heart should beat, that 

 his lungs should expand and contract, that certain secretions 

 should be manufactured, and that certain muscular movements 

 of his digestive organs should take place. In addition to 

 these involuntai-y actions, it is also desirable that he should 

 perform certain voluntary movements, such as standing, walk- 

 ing, and using his arms, legs, and body in a variety of ways. 

 All these actions, voluntarj' and involuntary, can onlj' be carried 

 out at the expense of definite amounts of energy, which must 

 be conveyed into the body in the form of food, just as the 

 energy to run a steam engine must be put into the engine 

 in the form of fuel. Now, before a steam engine can convert 

 the energy of its fuel into work, the fuel must be burned 

 to carbon dioxide and water, and the value of any kind of fuel 

 for the purpose of driving a steam engine can be, and is 

 commonly measured, by measuring the number of units of 

 heat, or calories as they are called, which one pound of that 

 fuel can give out when it is burned. In obtaining the energy 

 out of his food, a man slowly burns or oxidises the food to 

 carbon dioxide and water, the same products as those formed 

 in the furnace of a steam engine, and it follows, therefore, 

 that the energy-supplying value of a food can likewise be 

 measured by determining the number of calories given out 

 by burning one pound of it. As the result of many inquiries, 

 both experimental and statistical, it has l)een decided that 

 a man of average size can maintain his health on a diet which 

 supplies about 3,000 calories or heat units per day. The food, 

 however, must supply something beyond energy. To return 

 once more to the analogy of the steam engine, fuel alone will 

 not keep it going indefinitely. From time to time its working 

 parts will need repair. Coal or other fuels are useless for this 

 purpose. The working parts are made of iron or steel or brass, 

 and they can only be repaired by similar materials. In much 

 the same way, the working parts of the human body continually 

 need repair. These working parts, the muscles, nerves, glands, 

 and so fortli, are for the most part comi)osed of nitrogenous 

 substances, classed together under the name protein, and they 

 can only be repaired by the inclusion in the diet of sufficient 

 protein to provide tlie raw material to make good their waste. 

 It is commonly acce])ted that the least amount of protein 



