EXERCISE 79 



The circulating fluid, the blood, is inclosed in a system of tubes, arteries, veins, and capillaries. 

 The motion of the stream is caused by the pumping (muscular contraction) of the heart through which 

 the stream passes. The action of the heart is influenced by the chemical condition of the blood, and 

 this in turn is influenced by our breathing and by the work of the body. 



Problem. How does moderate exercise influence the rate of the heart's beat ? 



What to use. Chart for keeping record of class. 

 What to do. As the teacher keeps time for one minute, count the number of heart beats (pulse) 

 during the interval. 1 After brisk two-minute drill or setting-up exercise, count the pulse as before for 

 one minute. 



Record your own pulse : Before exercise After exercise 



Record. In the table below enter the number of students whose pulse was below 75 per minute 

 before exercising, the number whose pulse was between 76 and 80 inclusive, and so on. Then record 

 in the same way the pulse rates after exercising. 2 



Questions. 1. What is the lowest pulse rate of the class before exercising? after exercising? 



2. What is the highest pulse rate before exercising ? after exercising ? 



3. What is the average pulse rate for the class before exercising ? after exercising ? 



4. What chemical changes are brought about in the blood by exercising ? 



5. What besides exercise can make your pulse become faster or slower ? 



6. What changes do these things cause in the chemical condition of the blood ? 



7. What is the advantage or disadvantage of a changing pulse rate during exercise ? 



1 You can easily find your pulse by pressing your finger directly in front of your ear. 



[85] 



2 See note in Exercise 67. 



