428 Our Surroundings 



The pulse is a throb caused by the movement of the blood in 

 the arteries. The rate and strength of heart beat may be meas- 

 ured by the pulse. 



The blood makes a complete circuit, passing through the four 

 parts of the heart, the arteries, veins and capillaries. 



The lymphatics are a series of pipe-like vessels similar to 

 capillaries but smaller. They carry lymph. The lymphatics aid in 

 getting waste material into the blood current and in conveying the 

 fatty food from the intestines to the blood. 



Good circulation promotes health. Exercise promotes good 

 circulation. 



The use of alcohol may cause fatty degeneration of the heart, 

 paralysis of the heart nerves, dilation of the blood vessels and 

 injury to the white blood corpuscles. 



The use of tobacco makes the heart's action irregular. In the 

 young, particularly, it checks physical and mental development. 



Assimilation is the process of changing digested food into 

 tissue after it enters the cells. 



Excretion is the process of throwing off the waste substances 

 of the body. 



The organs of excretion are the kidneys, the lungs, the liver, 

 the skin and the large intestine. 



The importance of excretion to the health cannot be over- 

 estimated. Drinking plenty of water, bathing the body and 

 daily elimination of all wastes are essential to the maintenance 

 of health. 



FACT AND THOUGHT QUESTIONS 



1. Describe the structure of the heart. 



2. State how the heart is adapted by structure to do its work. 



3. How does the structure of an artery differ from the structure of a vein ? 



4. Trace the course of the blood in the systemic circulation. 



5. Give the functions of the circulation of the blood. 



6. What changes occur in the blood during its circulation? 



7. Describe an experiment to show variation in the pulse. 



8. State the effect of the habitual use of alcoholic drink on the heart. 



9. Describe the effect of the habitual use of tobacco on the heart. 



10. Describe the position, structure and chief function of the arteries. 



11. From what blood vessels are digested nutrients given to the tissues? 



