The Mind. 985 



of a complicated nature or of nnv occurrence, we are conscious of more 

 or less delay before a conclusion is reached. If the ether of our nervous 

 mid cerebral tissues were anything like as nimble and responsive to the 

 impact of force as is the hypothetical ether whose undulations arouse in 

 us the sensation of light, the time required for an external stimulation 

 to pass through our nervous and cerebral apparatus producing sensation, 

 perception, and final!}' expression, would be so short as to be immeas- 

 urable. But the material of our nervous system has no such mobility 

 as that of the free ether, and measurable time is required for all our 

 mental processes, even those which are most habitual and the nearest 

 being frictionless. The time required is greater in some persons than 

 in others, and in the same person it is greater for some sorts of stimu- 

 lation than for others; it is usually shorter with women and longer with 

 children than with men. The time is shortened by practice, habit mak- 

 ing the tissues concerned more mobile and responsive to the stimulation. 

 According to experiments of Prof. Exner, the usual time required for a stim- 

 ulus to produce a response in muscular expression is for ton eh sensations 

 about one-seventh of a second; hearing, one-sixth; sight, one-fifth; taste, 

 from one-sixth to one-fourth of a second. The differences are due to the 

 different lengths of nerve to be traversed, and the different activities in 

 the co-ordinating ganglia which lie between the afferent and the efferent 

 nerves. The sight ganglia appear to be slower in making up their co- 

 ordinations than the other ganglia, since it appears that although their 

 nerves are the shortest, the time they require in the aggregate is longer 

 than the others, except taste. After making allowance for the time oc- 

 cupied by the stimulation in traversing the nerve up and back, Prof. 

 Exner found that it took the ganglia of sight from the one-twenty-first 

 to one-eighteenth part of a second to turn the stimulation from an affer- 

 ent to an efferent current, the action being the closing of the eyelid 

 after a sight stimulation. The more complex the object seen, the 

 longer it takes to accomplish the co-ordination; the fact being that a 

 complex object is in reality several objects, and sight stimuli are, there- 

 fore, usually less simple than those which affect the other senses. In 

 these experiments when the co-ordination was complicated by presenting 

 two different stimuli at the same time, one of which was to be ignored 

 and the other responded to, the hesitation became from twice to four 

 times as long. Of course the general drill of education furnishes bet- 

 ter equipped ganglions for unexpected stimulations. In an old man of 

 76 of an inactive mental habit a certain stimulation took almost a whole 

 second for its co-ordination. After six months' practice the time was 

 reduced to less than one-fifth of a second. Romanes mentions the case 

 of Houdin, the great conjuror, who became so exceedingly rapid in ab- 

 sorbing and condensing sight stimuli, that on one occasion ho ropoatod 



