THE CHARACTERISTICS OF LIVING THINGS 21 



of movement, (%} need of food. (3) powejjQjLgmffiiwg, 

 frnm 



of rej3n)duing. All these activities or changes are found in 

 living plants and animals and none of them in lifeless bodies. 

 These are life-activities characteristic of living things. 



We see, then, that in order to distinguish accurately 

 between living and lifeless things we must determine whether 

 there are evidences of life-activities. Every year dealers 

 in seeds, gardeners, farmers, and the scientists at the govern- 

 ment laboratories must test samples of seeds in order to 

 determine whether they are living or lifeless. Chemical 

 analysis will not settle such a question; and so the only 

 way to test seeds is to put them under conditions where some 

 or all the life-activities may be manifested. In short, the 

 seeds must be planted under conditions favorable for growth. 

 Likewise dormant animals must be carefully examined for 

 evidences of life. For example, small animals of certain 

 species which are often abundant in soil where pools of 

 water have dried up in midsummer may appear perfectly 

 dead when viewed with the microscope ; but they begin to 

 move, eat, and manifest other life-activities soon after they 

 are placed in water. 



30. The Machinery of Life-Activities. We have seer* 

 that certain activities in animals and plants make the living 

 things different from the lifeless; and we shall now inquire 

 concerning the stucture and working of the living machinery 

 which in the animal or the plant moves, takes food, breathes, 

 grows, and reproduces. But in order to understand the 

 working of any complicated machinery, we must first take it 

 to pieces and examine its structure, and later find out the 

 use and work of each part. To this end we shall now examine 

 with considerable care the structure of an animal, and later 

 that of a plant. 



31. Subdivisions of Biology. The science of the structure 

 of animals and plants is called anatomy or morphology. 



