78 THE STORY OF THE LIVING MACHINE. 



pound as the basis of all living phenomena gave 

 rise in a short time to a chemical theory of life 

 which was at least tenable, and which accounted 

 for the fundamental properties of life. That 

 theory, the chemical theory of life, may be outlined 

 somewhat as follows: 



The study of the chemical nature of sub- 

 stances derived from living organisms has devel- 

 oped into what has been called organic chemis- 

 try. Organic chemistry has shown that it is pos- 

 sible to manufacture artificially many of the com- 

 pounds which are called organic, and which had 

 been hitherto regarded as produced only by living 

 organisms. At the beginning of the century, it 

 was supposed to be impossible to manufacture by 

 artificial means any of the compounds which ani- 

 mals and plants produce as the result of their life. 

 But chemists were not long in showing that this 

 position is untenable. Many of the organic prod- 

 ucts were soon shown capable of production by ar- 

 tificial means in the chemist's laboratory. These 

 organic compounds form a series beginning with 

 such simple bodies as carbonic acid (CO 2 ), water 

 (H 2 O),and ammonia (NH 3 ),and passing up through 

 a large number of members of greater and greater 

 complexity, all composed, however, chiefly of the 

 elements carbon, oxygen, hydrogen, and nitrogen. 

 Our chemists found that starting with simple sub- 

 stances they could, by proper means, combine 

 them into molecules of greater complexity, and in 

 so doing could make many of the compounds 

 that had hitherto been produced only as a result 

 of living activities. For example, urea, formic 

 acid, indigo, and many other bodies, hitherto pro- 

 duced only by animals and plants, were easily 

 produced by the chemist by purely chemical meth- 



