208 RESPIRATION, BLOOD, AND EXCRETION 



Arterrj 



uriniferous 

 tubule 



Figure 221. — Diagram. 



Showing relation of artery and 

 vein to portion of minute kidney 

 tube (uriniferous tubule). 



blood capillaries. At the 

 place where this close re- 

 lation takes place, glomeru- 

 lus (glo-meVu-lus), the 

 walls of the capillary and 

 the walls of the kidney are 

 very thin. Through these 

 thin walls a large amount 

 of water filters out of the 

 blood into the tubes. At 

 the same time waste ma- 

 terial which contains nitro- 

 gen, salts, and other organic 



wastes is removed. If these wastes are not removed, 



they create toxins which poison the body. 



SUMMARY 



All living things breathe oxygen which, in the higher 

 animals, is carried by the blood to the cells of the body. 

 The parts which man uses in breathing are more highly de- 

 veloped than in any other animal. Man has a voice box, the 

 larynx, by means of which he is able to make a wide variety 

 of sounds. The blood of man is similar to the blood of all 

 the other vertebrates, although not identical. It consists of 

 red and white corpuscles which move freely in the plasma. 

 The blood is confined in the blood vessels through which it 

 is forced by the heart. Excretion includes the waste 

 products derived from living protoplasm. The kidneys 

 and sweat glands remove the liquid wastes from the 



blood. 



QUESTIONS 



Compare the respiration of man, the hydra, and the earthworm. Com- 

 pare the lungs of man with the gills of a fish. What is blood ? What 

 is its use ? What is the difference between veins and arteries ? Explain 

 the work of the kidneys and of the lungs 



