176 THE BLOOD AND ITS CIRCULATION 



Summary. — The blood has been shown to be more than a mix- 

 ture of diffusible food substances, although one of its chief functions 

 is to carry food to the body cells. In addition the red corpuscles 

 exchange oxygen for carbon dioxide with the tissue cells. The 

 plasma also carries antibodies, substances which fight disease- 

 causing bacteria. In addition some of these antibodies (as the 

 opsonins) assist the colorless corpuscles to rid the body of bacteria. 

 Perhaps most important of all, the blood carries the regulating 

 hormones, manufactured in the endocrine glands, on the presence 

 of which the smooth running of our bodily activity depends. 



The heart has been shown to be a double force pump, which 

 sends the blood in two circulations through the body. The pul- 

 monary circulation carries the blood to and from the lungs ; the 

 systemic takes it to and from all other parts of the body. The 

 arteries, capillaries, and veins are the connecting tubes through 

 which the blood circulates. 



Fluid food and oxygen reach the tissue cells in the lymph which 

 bathes them, and wastes, both liquid and gaseous, are taken away 

 by the lymph. 



"Problem Questions 



1. Is the blood a tissue ? Why? 



2. What is the function of the red corpuscles ? Of colorless corpuscles ? 



3. What is the composition of plasma? How do you account for this? 



4. How does lymph differ from plasma ? 



5. What is one of the disease-resisting mechanisms of the blood and how 

 does it work? 



6. What are hormones ? What do they do ? How do they do it ? 



7. Prove that the heart is a force pump, 



8. Compare the short and long circulations in the body. 



9. How do cells get food and get rid of wastes? How do they "breathe" ? 



Problem and Project References 



Hunter, Laboratory Problems in Civic Biology. American Book Company. 

 Broadhurst, How We Resist Disease. Lippincott Company. 

 Burton-Opitz, Physiology. W. B. Saunders Company. 

 Harrow, Glands in Health and Disease. E. P. Button and Company. 

 Martin, The Human Body, Advanced Courses. Henry Holt and Company. 

 Sharp, Foundation of Health. Lea and Febiger. 



