FOODS. 123 



vaso-constrictor nerve-centers and certain areas of the brain, as shown by 

 an impairment in the power of sustained attention, clearness of judgment, 

 and muscle coordination. 



Alcohol is undoubtedly oxidized in the body, as only about 2 per cent, 

 can be obtained from the urine and expired air. It thus contributes to the 

 store of the body-energy. Whether for this reason it can be regarded 

 as a food that is, whether it can be substituted in part at least for fat or 

 carbohydrate material without impairing the protein metabolism is at 

 present a subject of experimentation and discussion. According to some 

 investigators, alcohol does not retard protein metabolism, for when it is 

 introduced into the body in amounts equivalent to the carbohydrates with- 

 drawn from the food there is at once a rise in the amount of nitrogen excreted. 

 Hence it cannot be regarded as a food. According to other investigators, 

 alcohol retards or protects protein metabolism just as effectually as an 

 equivalent amount of starch or sugar. Many more experiments are required 

 to decide this question. When taken habitually in large quantities, alcohol 

 deranges the activities of the digestive organs, lowers the body temperature, 

 impairs muscle power, lessens the resistance to depressing external con- 

 ditions, diminishes the capacity for sustained mental work, and leads to the 

 development of structural changes in the connective tissues of the brain, 

 spinal cord, and other organs. In infectious diseases and in cases of depres- 

 sion of the vital powers it is most useful as a restorative agent. 



THE ENERGY OR HEAT VALUE OF THE FOOD PRINCIPLES. 



The food consumed not only restores the material metabolized and 

 discharged from the body, but also the energy which has been expended as 

 heat and mechanic motion. The food principles are products of the con- 

 structive processes taking place in the vegetable world during the period of 

 growth and activity. At the time of their formation there is an absorption 

 and storing of the sun's energy which then exists in a potential condition. 

 During the metabolism of the animal body these compounds are reduced 

 through oxidation to relatively simple bodies, such as carbon dioxid, water, 

 urea, etc., with the liberation of their contained energy. All of the energy 

 of the body, whatever" its manifestations may be, can be traced to chemic 

 changes going on in the tissues, and more particularly to those changes 

 involved in the oxidation of the food principles. 



It becomes, therefore, a matter of interest to determine the heat loss 

 from the body in twenty-four hours for the purpose of subsequently deter- 

 mining if the energy contained in the foods, expressed in terms of heat, is 

 present in amounts sufficient to compensate for the loss. The total quan- 

 tity of heat liberated in the body and dissipated from it in twenty-four hours 

 is determined by placing the subject in a respiration chamber provided with 

 appliances containing water, by means of which the heat can be absorbed 

 and measured. (See chapter on Animal Heat.) The unit of heat measure- 

 ment is the Calorie, which is defined as the amount of heat necessary to raise 

 the temperature of one kilogram of water i C. If therefore the volume 

 of the water employed in the experiment expressed in kilograms be multi- 

 plied by the number of degrees of temperature through which it has been 



