290 PHYSIOLOGY OF MUSCLES AND NERVES. 



This sluggishness of the consciousness, if we may so 

 call it, is exhibited in another way in certain experi- 

 ments instituted by Helmholtz. ^ The eye sees a iigure, 

 which is immediately followed by a bright light : the 

 more powerful the latter is, the longer must the first 

 have been seen, if it is to be recognised at all ; more- 

 over, complex figures require more time than simpler. 

 If letters are seen lighted up on a bright ground for a 

 very short time, no other light following, a shorter time 

 is necessary for the recognition, the larger are the letters 

 and the brighter the illumination. 



It is true that it is only very simple brain activities 

 the origin of which can be in any way made clearer by 

 such experiments as these ; but yet these are the rudi- 

 ments of all mental activity — sensation, conception, re- 

 flection, and will; and even the most elaborate deduction 

 of a speculative philosopher can only be a chain of such 

 simple processes as those which we have been observ- 

 ing. These measurements, therefore, represent the 

 beginnings of an experimental physiological psychology, 

 the development of which is to be expected in the 

 future. It seems to me that remunerative study of 

 the processes in nerve-cells must start from the very 

 simplest phenomena. Eesults are, therefore, to be first 

 looked for in the study of the processes of reflection ; 

 possibly these Avill prepare the ground on which at some 

 future time a mechanism of the nervous processes may 

 be built. ' In truth,' says D. F. Strauss, in ' The Old 

 and the New Faith,' ' he who shall explain the grasp 

 of the polyp after the prey which it has perceived, or 

 the contraction of the insect larva when pierced, will 

 indeed be yet far from having in this comprehended 

 human thought, but he will be on the way to do so, and 



