36 THE VITAL PROCESSES 



wholesome food, pure water, outdoor exercise and sunlight, 

 plenty of sleep, and a clean skin for keeping the blood in 

 good condition. If these natural remedies fail, a physician 

 should be consulted. 



Summary. The blood is the carrying or transporting 

 agent of the body. It consists in part of constituents, such 

 as the red corpuscles, that enable it to carry different sub- 

 stances ; and in part of the materials that are being carried. 

 The latter, which include food and oxygen for the cells and 

 wastes from the cells, may be classed as freight. Certain 

 constituents in the blood destroy disease germs, and other 

 constituents, by coagulating, close small leaks in the blood 

 vessels. Although subject to rapid and continuous change, 

 the blood is able by reason of the balancing of materials 

 added to 'and withdrawn from it to remain about the 

 same in quantity and composition. 



Exercises. i . Compare blood and water with reference to weight, 

 density, color, odor, and complexity of composition. 



2. Show by an outline the different constituents of the blood. 



3. Compare the red and white corpuscles with reference to size, 

 shape, number, origin, and function. 



4. Name some use or purpose for each constituent of the blood. 



5. What constituents of the blood may be regarded as freight and 

 what as agents for carrying this freight ? 



6. After coagulation, what portions of the blood are found in the 

 clot ? What portions are found in the serum ? 



7. What purposes are served by water in the blood ? 



8. Show how the blood, though constantly changing, is kept about . 

 the same in quantity, density, and composition. 



9. In the lungs the blood changes from a dark to a bright red color 

 and in the tissues it changes back to dark red. What is the cause of 

 these changes ? 



10. If the oxygen and hemoglobin formed a strong instead of a 

 weak chemical union, could the hemoglobin then act as an oxya en car- 

 rier ? Why ? 



