CHAPTER XXII 

 LIVING MATTER 



273. Physiological Properties. Plants and animals are 

 made up of matter, and have certain physical properties, 

 such as weight and extension, which are possessed by all 

 matter. In addition to physical properties, both plants and 

 animals possess certain properties which never belong to 

 non-living matter. These are called physiological properties; 

 they are irritability, spontaneous motion, reproduction, and 

 nutrition. Any body possessing these properties is called an 

 organism, and much of the material of which it is composed 

 is called organic material. 



274. Irritability. Both plants and animals respond to 

 influences from without. For example, leaves turn toward 

 the source of light, and the odor of food will make a dog's 

 mouth water. This property of responding to external 

 conditions is called irritability. 



275. Spontaneous Motion. Both plants and animals 

 have the power to change the position of parts of the body 

 or the whole body. This is the property of spontaneous 

 motion. A fish darts rapidly or moves slowly through the 

 water at will. Plants move their leaves, stems, flowers, or 

 other parts, but generally so slowly as to be unnoticed in 

 brief observation. 



276. Reproduction. Both plants and animals possess the 

 property of reproduction; that is, they can form other bodies 

 like themselves. For example, the bean plant reproduces by 

 means of seeds, and the fish by means of eggs. 



277. The Need of Energy. These three properties 

 irritability, spontaneous motion, and reproduction con- 



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