2. State the necessity for a circulating liquid in the body. 3. Show by a drawing the general plan of the heart, locating and naming the essential parts. Show also the connection of the large blood vessels with the cavities of the heart. 4. Compare the purpose served by the chordæ tendineæ to that served by doorstops (the strips against which the door strikes in closing). 5. Explain how the heart propels the blood. To what class of pumps does it belong? What special work is performed by each of its divisions? 6. Define a valve. Of what use are the valves in the heart? In the veins? 7. By what means is pressure from contracting muscles in different parts of the body made to assist in the circulation? 8. Of what advantage is the elasticity of the arteries? 9. How is blood forced from the capillaries back to the heart? 10. Why should there be a difference in structure between the two sides of the heart? 11. Following Fig. 23, trace the blood through a complete circulation, naming all the divisions of the system in the order of the flow of the blood. 12. If the period of rest following the period of contraction of the heart be as long as the period of contraction, how many hours is the heart able to rest out of every twenty-four? 13. State the functions of the capillaries. Show how their structure adapts them to their work. 14. What kind of physical exercise tends to strengthen the heart? What forms of exercise tend to injure it? State the effects of alcohol and tobacco on the heart. 15. How may rheumatism injure the heart? 16. Give directions for checking the flow of blood from small and from large blood vessels. PRACTICAL WORK In showing the relations of the different parts of the heart, a large dissectible model is of great service (Fig. 24). Indeed, where the time of the class is limited, the practical work may be confined to the study of the heart model, diagrams of the heart and the circulation, and a few simple experiments. However, where the course is more extended, the dissection of the heart of some animal as described below is strongly advised. *Observations on the Heart.*—Procure, by the assistance of a butcher, the heart of a sheep, calf, or hog. To insure the specimen against mutilation, the lungs and the diaphragm must be left attached to the heart. In studying the different parts, good results will be obtained by observing the following order: 1. Observe the connection of the heart to the lungs, diaphragm, and large blood vessels. Inflate the lungs and observe the position of the heart with reference to them.