IS THE BODY A MACHINE? 63 



been able to reach a satisfactory positive 

 answer. Digestion, assimilation, circulation, 

 respiration, excretion, the principal categories 

 of physiological action, and at least certain 

 phases of the action of the nervous system are 

 readily understood as controled by the action 

 of chemical and physical forces. In the accom- 

 plishment of these actions there is no need 

 for the supposition of any force other than 

 those which are at our command in the scientific 

 laboratory. 



THE LIVING MACHINE CONSTRUCTIVE AS WELL AS 

 DESTRUCTIVE. 



In one respect the living machine differs from 

 all others. The action of all other machines re- 

 sults in the destruction of organised material, and 

 thus in a degradation of matter. For example, a 

 steam engine receives coal, a substance of high 

 chemical composition, and breaks it into more 

 simple compounds, in this way liberating its 

 stored energy. Now if we examine all forms 

 of artificial machines, we find in the same way 

 that there is always a destruction of compounds 

 of high chemical composition. In such machines 

 it is common to start with heat as a source of 

 energy, and this heat is always produced by the 

 breaking of chemical compounds to pieces. In 

 all chemical processes going on in the chemist's 

 laboratory there is similarly a destruction of 

 organic compounds. It is true that the chemist 

 sometimes makes complex compounds out of 

 simpler ones; but in order to do this he is 



