THE LIVING MACHINE BUILDING FACTORS. 213 



know nothing. Irritability, movement, metabo- 

 lism, and reproduction appear to be not chemical 

 properties of a compound, but mechanical pro- 

 perties of a machine. Our mechanical analysis 

 of the living machine stops short before it 

 reaches any foundation in the chemical forces 

 of nature. 



It is thus clearly apparent that the pheno- 

 mena of life are dependent upon the machinery 

 of living things, and we have therefore the 

 second question of the origin of this machinery 

 to answer. Chemical forces and mechanical 

 forces have been laboriously investigated, but 

 neither appear adequate to the manufacture of 

 machines. They produce only chemical compounds 

 and worlds with their mountains and seas. The 

 construction of artificial machines has demanded 

 intelligence. But here is a natural machine the 

 organism. It is the only machine produced by 

 natural methods, so far as we know; and we 

 have, therefore, next asked whether there are, in 

 nature, simple forces competent to build machines 

 such as living animals and plants ? 



In pursuance of this question we have found 

 that the complicated machines have been built 

 out of the simpler ones by the action of known 

 forces and laws. The factors in this machine 

 building are simply those of the fundamental 

 vital properties of the simplest protoplasmic 

 machine. Reproduction, heredity, and variation, 

 acting under the ever-changing conditions of the 

 earth's surface, are apparently all that are needed 

 to explain the building of the complex machines 

 out of the simpler ones. Nature has forces ade- 



