HYGIENIC ASPECTS OF NUTRITION 361 



contamination, thorough cooking should always precede the 

 introduction of food into the body. The body is a machine, 

 and food is the material that builds it up and supplies the 

 energy to run it. Filth and disease bacteria interfere with 

 the normal work and efficiency of the machine. 



368. Circulation and nutrition. The role of the circulation 

 in carrying digested food to the tissues has already been 

 discussed. It must be clearly understood, therefore, that 

 anything which makes the circulation abnormal will affect 

 nutrition. In most adults the heart beats about seventy-two 

 times per minute. In children and youths the rate is likely 

 to be higher, while in old people it may be lower. By plac- 

 ing a finger upon the inside of the wrist one can usually 

 feel the pulse, which tells accurately how many times per 

 minute the left ventricle is contracting. Count your pulse 

 beats during each of several minutes and determine what 

 the normal average is. 



During severe exercise increased release of energy takes 

 place, and there is increased demand for oxygen and food. 

 This results in increased heart action. In some cases of 

 severe illness during high fever a similar demand is made, 

 with a similar increase of heart action. Prolonged increase 

 above the normal rate means excessive wear upon the parts 

 of the human machine that are affected. A brief period of 

 this unusual stimulation is not necessarily harmful and may 

 often be decidedly helpful. 



369. Breathing and nutrition. Experiments similar to those 

 suggested in connection with circulation will enable one to 

 determine that the normal breathing rate is about sixteen 

 times per minute and also that violent exercise increases 

 the rate. The tissues demand oxygen, which is secured from 

 the blood. The blood's supply of oxygen is replenished in the 

 lungs, where the waste carbon dioxide is removed. When 

 an increased amount of blood needing replenishment and 

 purification is hastened through the lungs, there is need of 



