CHAPTER I 

 THE WORLD OF LIFE 



Every one recognizes that plants and animals are living things ; 

 the study of plants constitutes the science of botany, while the 

 science of zoology (Gr. £wov, animal, and Xo'yo?, discourse) con- 

 cerns itself with the study of animals ; the term biology, the 

 science of life, may be used to include them both. So far as 

 our present knowledge goes, no living matter can come into 

 existence from lifeless matter ; every plant has been derived 

 from some other plant, and every animal has developed from 

 some other animal ; the spontaneous generation of life from 

 the lifeless was a theory long believed, but for which there is 

 no foundation of fact in science to-day. Whether in the history 

 of the world living matter may ever have arisen from lifeless 

 matter we are not prepared to say ; it is, however, very proba- 

 ble that such was the case, but we have no evidence in fact 

 that any life at present on the earth has come into existence 

 except from preexisting life. On the other hand, living matter 

 appears to be subject to the same chemical and physical laws 

 as lifeless matter, but the former exhibits certain phenomena 

 which we call life, which are absent from the latter; life is 

 probably due to some peculiar arrangement of the most minute 

 constituent parts of certain combinations of chemical elements, 

 so that forms of energy are brought into play which produce 

 the phenomena of life and are absent or inert in lifeless matter. 

 This theory is substantiated by the fact that, in the analysis of 

 living matter, the weight of the substances obtained is the same 

 as the weight of the living body, although for the purpose of 

 analysis the organism must be killed. Life, then, is not a 

 material substance, it has no weight, it is a condition of matter. 



The peculiar properties of living matter are (i) its ability to 



