OUTLINES OF EVOLUTIONARY 

 BIOLOGY 



PART I. THE STRUCTURE AND FUNCTIONS 

 OF ORGANISMS THE CELL THEORY 



CHAPTER I 



Introductory : The nature of life The living organism viewed as a machine 

 The essential functions of the living body The source of energy in 

 living things. 



THERE are many ways in which the extremely heterogeneous 

 materials of which the earth is composed may be classified. 

 Physicists often speak of them as solid, liquid or gaseous 

 respectively, but we know that one and the same substance may 

 exist in any of these conditions, changing from one to the other 

 in accordance with changing conditions of temperature and 

 pressure. Chemists, on the other hand, tell us that all sub- 

 stances are made up of certain definite chemical elements, 

 occurring free or in a state of combination with one another, 

 and that the almost infinite variety of gases, liquids and solids 

 with which we are familiar has arisen mainly from this power 

 of combination in very diverse but perfectly definite ways. The 

 tendency of modern research, however, is to show that even the 

 so-called chemical elements are not really so elementary in their 

 nature as has been supposed, and it is quite conceivable that 

 they may all have a common origin. 



Our present purpose is to investigate a condition of matter 

 which altogether transcends the classifications of the chemist 

 and the physicist, a condition in which it exhibits those peculiar 

 phenomena which we regard as manifestations of Life, and the 

 study of which constitutes the science of Biology. It is not 



