CELLS AND THE CELL THEORY 41 



a long search for a chemical explanation of life phenomena. 

 In accordance with this idea, life was looked upon as merely 

 representing a special manifestation of chemical and physical 

 forces; it was argued that there was no more reason to speak of 

 vitality as a special property possessed by living things, than to 

 speak of aquosity as a special property possessed by the chemical 

 compound water. 



The Mechanical Theory of Life. Based upon this conception 

 arose a large number of interesting speculations, and the discus- 

 sions during the next twenty-five years resulted in a develop- 

 ment of the mechanical theory of life. It was argued that, if 

 life is merely a name given to the properties of protoplasm, and if 

 chemists could manufacture the chemical substance protoplasm, 

 they could thus create life, i.e., living protoplasm. Chemistry 

 was at this time advancing with prodigious strides, and chemists 

 were making more and more complex substances, and new com- 

 pounds which had hitherto been considered beyond their reach. 

 Many of the substances, which had previously been supposed to 

 be produced only by living processes, were, one by one, manufac- 

 tured synthetically in the chemist's laboratory. From this the 

 further assumption and confident prediction was made that the 

 time would come when it would be possible to manufacture a bit 

 of protoplasm by purely chemical means; and then it would fol- 

 low, if the mechanical theory of life were correct, that this bit of 

 protoplasm would necessarily be alive and scientists would thus 

 be able to manufacture a living thing. This was the essence of 

 the mechanical theory of life which largely dominated discussion 

 of biology for a quarter of a century. 



General Properties of Protoplasm. With this idea of pro- 

 toplasm as the basis of life, a large amount of study was given 

 to this interesting material. Since it is alive, it has of course 

 all the properties of life. If we look upon protoplasm as the 

 physical basis of life, we may in one sense say that its proper- 

 ties are as varied as are the properties of living things, since 

 the characteristics of living things are based upon the charac- 



