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that contain it are connected with the system for the circulation of the blood. By adding new material to the lymph and withdrawing waste material from it, the blood keeps this liquid in a suitable condition for supplying the needs of the cells. Supplementing each other in all respects, the blood and the lymph together form the nutrient cell fluid of the body. The interchange of material between the blood and the lymph, and the lymph and the cells, takes place in part according to the principle of osmosis. *Exercises.*--1. Explain the necessity for the lymph in the body. 2. Compare lymph and water with reference to density, color, and complexity of composition. 3. Compare lymph and blood with reference to color, composition, and movement through the body. 4. Show how blood pressure in the capillaries causes a flow of the lymph. 5. Show how contracting muscles cause the lymph to move. Compare with the effect of muscular contraction upon the blood in the veins. 6. Trace the lymph in its flow from the right hand to where it enters the blood; from the feet to where it enters the blood. 7. What conditions prevail at the cells to cause a movement of food and oxygen in one direction and of waste materials in the opposite direction? 8. What part does water play in the exchanges at the cells? 9. Show that the blood and the lymph together fulfill all the requirements of a nutrient cell fluid in the body. PRACTICAL WORK *To illustrate the Effect of Breathing upon the Flow of Lymph.*--Tightly holding one end of a glass tube between the lips, let the other end extend into water in a tumbler on a table. In this position quickly inhale air through the nostrils, noting that with each inhalation there is a slight movement of the water up the tube. (No sucking action should be exerted by the mouth.) Apply to the movements in the large blood and lymph vessels entering the thoracic cavity. *To illustrate Osmosis.*--1. Separate the shell from the lining membrane at one end of an egg, over an area about one inch in diameter. To do this without injuring the membrane, the shell must first be broken into small pieces and then picked off with a pair of forceps, or a small knife blade. Fit a small glass tube, eight or ten inches long, into the other end so that it will penetrate the membrane and pass down into the yolk. Securely fasten the tube to the shell by melting beeswax around it, and set the egg in a small tu
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