150 BLOOD AND ITS IMPORTANCE 



deal of heat is generated in active tissues such as muscular tissue 

 and the liver, and the surplus heat must be distributed to passive 

 tissues. Very little heat is generated in passive tissues such as 

 bone, so heat must be sent to them by the blood when needed. 

 The blood system may be compared to a hot- water system. The 

 muscles are like little furnaces in which burning takes place. This 

 heats the surrounding blood. As the blood circulates it radiates 

 heat to the tissues that need it, and thus keeps the temperature of 

 the body constant at ninety-eight and six tenths degrees Fahrenheit 

 (98.6 F.). When glands give off secretions and have no ducts for 

 draining the secretions, the blood absorbs them. 



In brief, the functions of blood are nutritive, protective, and 

 excretory. When scientists can supply the same conditions to 

 tissues outside of the body as those provided by the blood, tissues 

 can be kept alive under experimental conditions outside of the 

 body. This was one of Carrell's big achievements. He experi- 

 mented for many years before he was able to duplicate the con- 

 ditions outside of the body that were found in the blood. When 

 he succeeded in doing this, he was able to grow tissues outside of 

 the body. His work has been previously discussed on page 54. 



QUESTIONS 



1. Defin^ oxygenated and deoxygenated blood. 



2. What is defibrinated blood ? 



3. Compare arterial and venous blood. 



4. Compare the red and white corpuscles in appearance, size, num- 

 ber, and function. Where are they made and where are they de- 

 stroyed ? 



5. Give six functions of blood. 



6. Why does blood clot ; why is blood clotting necessary ? 



