460 CHEMICAL DISCOVERY AND INVENTION 



In the plant the green colouring matter chlorophyll plays an 

 important part, the exact nature of which is not yet understood. 

 All that can be said at present is that it is not merely catalytic, 

 and that the efficiency of the green matter in association with the 

 living protoplasm in fixing carbonic acid is far greater than that 

 of any combination of inorganic materials yet tried. 



Researches of this kind have been connected, especially 

 during recent years, with speculations as to the origin of life. 

 Man finds himself in a world so full of miracles, and the daily 

 spectacle is so familiar as almost to paralyse the faculty of 

 wonder. Nevertheless the desire to form a theory or view as to 

 how it all came about has been in all ages and among all peoples 

 so urgent that in the absence of direct and positive knowledge 

 mythology has always centred round a special act of creation. 

 " In the beginning," when the earth was " void," that is empty, 

 it was filled with all manner of beast and bird and creeping thing, 

 and with the herb and tree which was to be their food. In no 

 case is the nature of the act of creation revealed, or what would 

 be called in modern language the physical or chemical acts or 

 doings by which the water and the dry land were furnished with 

 inhabitants. 



Geology assures us that there was a time when the earth was 

 at a temperature at which no living animal or vegetable could 

 exist. There is abundant evidence that as it cooled down it 

 gradually became clothed with a vegetation differing in form and 

 structure from that which now covers its surface, and with a 

 succession of animals of which the earliest were chiefly inhabitants 

 of the water, while the latest of all included man himself. 



From these facts and from the knowledge laboriously acquired, 

 chiefly during the last century, concerning the forms, the structure, 

 the habits, and mode of propagation of plants and of animals, the 

 doctrine of organic evolution has arisen, and with slight varia- 

 tion of detail has been accepted by the whole civilised world. 

 This doctrine teaches that the higher animals and plants possess- 

 ing more specialised organs and internal structure arose from 

 lower, less specialised forms by a process which involved what 

 may be termed experimental trials by Nature, through the results 

 of spontaneous variation and survival of the fittest. The imagina- 

 tion of the naturalist then travels back from mammal to bird and 

 reptile, through fishes and Crustacea to sponges and corals, till 

 the animal can no longer be distinguished from the vegetable, 



