166 THE MECHANISM OF LIFE 



from the centre and dividing along two distinct nervous paths 

 as it approached the part that was to be set in action. Finally, 

 while all this was being made out, many investigators had been 

 tracing out the microscopic structure of the receptor organs, nerve 

 fibres, and centres, and also the structure of the muscles, while 

 others were working out the nature of the physical and chemical 

 changes that occur when nerve and muscle become active. 



We have still to find out exactly how the physical events that 

 occur outside the body affect the nerve terminations in the sense 

 organs; what is the nature of the nervous impulse itself; what 

 kind of change it produces in the nervous centres; and what are 

 the energy transformations that occur in the muscle when the 

 fibres of the latter shorten or contract. There is no doubt at 

 all that these things will soon become known, and that our 

 analysis of the sensori-motor activity will become much finer 

 than it is. From the point of view of human progress this 

 analysis is all-important, for upon it depends whatever success 

 we shall attain in preventing disease and lengthening life; 

 obviously it is our knowledge of the working of the mechanism 

 that matters from the utilitarian standpoint. 



Now the reader cannot fail to see that the results of physio- 

 logical research are a description of the way in which things that 

 may happen in the animal body do happen, and that the descrip- 

 tion makes use of the same conceptions that physicists and 

 chemists use; no other results than these could possibly come 

 from an investigation that utilises chemical and physical methods, 

 and so, when we say that science finds nothing in life activities 

 but physico-chemical reactions, we mean that those reactions 

 are all that science looks for, or could possibly attempt to dis- 

 cover. We describe how things happen, but we do not explain 

 why they happen. Of course, it may be said that it is not the 

 business of science to ask why anything happens, but that is just 

 what ordinary people do ask, and it is the task of what we call 

 philosophy to try to answer the question. 



Science, then, no matter whether it be physical, chemical, or 

 " natural " science, investigates the ways in which things happen, 

 and it reduces all kinds of events to motions, or, rather, to dis- 

 placements. What does this mean ? the reader will ask. Well, 

 mechanics, in the first place, obviously considers nothing but 

 motions; it deals with material bodies having mass, and with 

 " forces " which " act upon " those bodies. But force is only 



