XXI. THE BLOOD AND ITS CIRCULATION 



Problems. — To discover the co7)%}:>osition and uses of the dif- 

 ferent parts of the blood. 



To find out the vveans by which the blood is circulated about 



the body. 



Laboratory Suggestions 



Demonstration. — Structure of blood, fresh frog's blood and human 

 blood. Drawings. 



Demonstration. — Clotting of blood. 



Demonstration. — Use of models to demonstrate that the heart is a 

 force pump. 



Demonstration. — Capillary circulation in web of frog's foot or tad- 

 pole's tail. Drawing. 



Home or laboratory exercise. — On relation of exercise on rate of heart- 

 beat. 



To THE Teacher. — To prove that blood contains liquid food and to show how 

 blood is made are the first considerations in this chapter. The uses of the cor- 

 puscles may well be shown in part by experiment. Proof of circulation of the blood 

 centers around two experiments : e\ddence that the heart is a force pump and the 

 demonstration of capillary circulation in the tadpole's tail. Interesting and vital 

 laboratory work may be done by comparing graphs of the heartbeat of members 

 of the class when at rest, after mental work, and after physical work. Interesting 

 correlations between physiologic age, sex, and rate of heartbeat may also be 

 worked out. The importance of ferments in the blood is a new and fascinating 

 topic to which time should be devoted if materials are available to the teacher. 



Problem 198 : To prove that blood contains nutrients. 



Materials. — Ox blood, nitric acid, ammonia, Fehling's solution, 

 formalin, iodine, test tubes, lamp, egg beater. 



Method. — Collect some blood at a slaughter house. Set 

 aside one bottle to clot (label it clotted blood). Place some of 

 the fresh blood in a flat bowl and beat it with an egg beater. Fill 

 a bottle with the red liquid (label it defibrinated blood). After 

 washing, place the fibrin, or threads which stick to the egg beater, 

 in a third bottle. Pour 4 per cent formalin on the fibrin to 



232 



