184 THE MECHANISM OF LIFE 



would say as much nowadays, this hypothesis exists in almost 

 as crude a form. " Consciousness," says Jacques Loeb, " is only 

 a metaphysical term for phenomena which are determined by 

 associative memory." " All life phenomena are ultimately due 

 to motions or changes occurring in colloidal substances. The 

 question is, which peculiarities of colloidal substance can make 

 the phenomena of associative memory possible ?" 



Now, what do we discover when we investigate the changes 

 in the colloidal substance of the nervous system that follow upon 

 sensation ? Obviously nothing but displacements, as we showed 

 on pp. 16770. A minute quantity of energy enters the body as 

 the result of the excitation of a receptor organ, and this energy 

 is transmitted along an afferent nerve as an impulse. What 

 becomes of it ? 



If the stimulus leads to a reflex, as when we involuntarily 

 contract the pupils of the eyes when we are suddenly exposed to 

 a bright light, then the thing is clear : the energy of the afferent 

 impulse is transmitted (still as a wave of molecular displace- 

 ments) through the visual and oculo-motor centres, along the 

 oculo-motor nerves, and into the muscles of the iris. There it 

 releases muscular energy, leading to contraction of the pupil. 

 Some of the energy (but a very small percentage) is doubtless 

 dissipated as heat during the nervous passage, just as it would 

 be in an ordinary physical process. There is no conscious per- 

 ception here, and we can account for all the energy put into the 

 sensation; but what are the circumstances when the stimulation 

 of a receptor organ gives rise to conscious perception, and also 

 leads to some muscular response ? Again, some of the energy 

 passes on to effect the releasing transformation, and again some 

 is dissipated. But an image, or mental representation (the per- 

 ception), also arises, and can we say that some of the energy trans- 

 forms into this ? That is to say, does physical energy, which we 

 measure as the displacements of material bodies as space magni- 

 tudes really transform into consciousness, or perception, which 

 is certainly not the displacement of material bodies, and cannot 

 be measured in terms of space ? No one ventures to say that. 



The perception has been called an " epiphenomenon," and has 



been compared with the luminous trail left by a meteorite which 



blazes up as it enters the earth's atmosphere; perhaps it is 



unnecessary to point out the difficulties of this explanation ! 



For the perception does not fade away when the action has 



