82 The Science of Life. 



This may seem by no means extraordinary to some, 

 but it is the beginning of a physiology of reproduction 

 in plants. 



Chapter VIII. 

 The Conditions of Life and Death. 



Three Periods of Opinion The Organism and the Inorganic World 

 The Quick and the Dead Characteristics of Living Organisms 

 "Vital Force" The Kinds of Death Organic Immortality 

 General Conditions of Life Origin of Life Ancient Belief in 

 Spontaneous Generation Mediceval Beliefs Red?s Experiments 

 Slow Death of the Theory of Spontaneous Generation Pouchet and 

 Pasteur Tyndall The Fact of Biogenesis Opinions as to the 

 Origin of Life upon the Earth. 



All vital activity implies interaction between the living 



creature and its surroundings, between the organism 



Three an( * * ts env i rc > nment j an ^ the most general 



Periods of problems of physiology have to do with this 



P inion - relation. 



(i.) In ancient times the relation of dependence in 

 which an organism stands to its environment was not 

 perceived, except in an occasional prophetic flash of 

 insight. Nor could it be otherwise until the advance 

 of chemistry and physics made an analysis of function 

 possible. It was also characteristic of the old days 

 that the contrast between the living and the not-living 

 was made little of; for the doctrine of the spontaneous 

 generation of even highly organized animals met with 

 general acceptance from Aristotle to Harvey. 



(2.) A second period, which we may date from the 

 discovery of oxygen, shows the growth of a conviction 

 that the organism is in part dependent upon its sur- 

 roundings. But this conviction was inhibited by the 

 theory of a special vital force, supposed to dominate 

 the chemical and physical processes which occur in a 

 living body. This theory was probably strengthened 



