OUR APPROACH 3 



all of the activities which have to do with the breakdown of 

 substance, and constructive metabolism including all the activi- 

 ties which have to do with the repair of waste and with growth. 



One of the remarkable consequences of the accumulation of 

 all of these facts regarding structures and functions of living 

 things, is the realization that all animals are fundamentally alike 

 rather than fundamentally different. If we could analyze any 

 one of the fundamental activities of living matter clear through 

 to the end in any one organism, it would be a simple step to apply 

 such knowledge to other organisms. Details would vary but the 

 functions are essentially the same. So it is with the fundamental 

 principles underlying modern study in genetics — principles 

 formulated from the study of heredity in the fruit fly (Droso- 

 phila) * are applicable to all types. In a similar way a great deal 

 of light may be thrown on the nature of the functions of higher 

 types of animals by the thorough study of the functions and ac- 

 tivities of the Smallest Living Things. 



Back in the 17th century, in the days of awakening imagina- 

 tion, when men were beginning to ask what is the meaning of 

 life and how does it arise, the English physician, William Har- 

 vey, the Italian physiologist, Francesco Redi, and other enlight- 

 ened naturalists of that age were experimenting independently 

 on different types of animals and were rapidly putting an end 

 to the current belief that flies and other common animals arise 

 from dirt or lifeless matter by so-called spontaneous generation. 

 As a result of such experiments it was demonstrated that flies lay 

 eggs which develop into maggots, and maggots turn into flies; 

 in other words that life comes from pre-existing life — a funda- 

 mental conception expressed by the aphorisms omne vivum ex 

 vivo and ex ova omnia. 



The First Appearance of Living Things 



Scientists have concluded that living things must have ap- 

 peared on the earth more than 1200 million years ago.t Evi- 

 dences of past life are afforded by the remains (usually structures 

 such as shells, skeletons, woody fiber, etc.) of animals and plants 

 embedded in some protective material which, subsequently, be- 



* See "Heredity and Variation," pages 51-66, in this Series. 

 t See "The Earth" and "Fossils" both in this Series. 



