52 THE STORY OF THE LIVING MACHINE. 



degradation of chemical compounds rather than a 

 construction. Constructive processes, which in- 

 crease the amount of high compounds in nature, 

 are confined to the living machine, and indeed to 

 one special form of it, viz., the green plant. This 

 constructive power radically separates the living 

 from other machines; for while constructive pro- 

 cesses are possible to the chemist, and while en- 

 gines making use of sunlight are possible, the liv- 

 ing machine is the only machine that increases 

 the amount of high chemical compounds in the 

 world. 



The Vital Factor. With all this explanation of 

 life processes it can not fail to be apparent that 

 we have not really reached the centre of the prob- 

 lem. We have explained many secondary pro- 

 cesses, but the primary ones are still unsolved. 

 In studying digestion we reach an understanding 

 of everything until we corne to the active vital 

 property of the gland-cells in secreting. In study- 

 ing absorption we understand the process until 

 we come to what we have called the vital powers 

 of the absorptive cells of the alimentary canal. 

 The circulation is intelligible until we come to 

 the beating of the heart and the contraction of 

 the muscles of the blood-vessels. Excretion is 

 also partly explained, but here again we finally 

 must refer certain processes to the vital powers 

 of active cells. And thus wherever we probe the 

 problem we find ourselves able to explain many 

 secondary problems, while the fundamental ones 

 we still attribute to the vital properties of the ac- 

 tive tissues. Why a muscle contracts or a gland 

 secretes we have certainly not yet answered. 

 The relation of the actions to the general prob- 

 lems of correlation of force is simple enough. 



