104: NERVOUS SYSTEM 



tion of acts involving the central nervous system, as the 

 reflex phenomena of the spinal cord or the operations of the 

 cerebral hemispheres. These have been partially successful, 

 or, at least, they have shown that the reflex and cerebral 

 acts require a distinctly appreciable period of time. This, 

 in itself, is an important fact ; though the duration of these 

 acts has not yet been measured with all the accuracy that 

 could be desired. As the general result of experiments upon 

 these points, it is found that the reflex action of the spinal 

 cord occupies more than twelve times the period required 

 for the transmission of stimulus or impressions through the 

 nerves. 1 Donders found, in experiments on his own person, 

 that an act of volition required one-twenty-eighth of a sec- 

 ond, and one of simple distinction or recognition of an im- 

 pression, one-twenty-fifth of a second. 2 These estimates, 

 however, are merely approximative ; and until they attain 

 greater certainty, it is unnecessary to describe in detail the 

 apparatus employed. 



The general result of the various observations we have 

 detailed upon the rate of nervous conduction as applied to 

 the human subject is, in the first place, that this can be 

 measured with tolerable accuracy.; second, that it is in no 

 wise to be compared with the rate of conduction of light or 

 electricity ; and, finally, that the rate in the human subject 

 is essentially the same in the motor and sensory nerves, be- 

 ing, according to the most reliable estimates, about one hun- 

 dred and eleven feet per second. 



Elevation of Temperature in Nerves during their Func- 

 tional Activity. There is little to note under this head, ex- 

 cept the fact that functional activity of the nerves produces 

 an amount of elevation to temperature in their substance 

 which can be distinctly demonstrated by sufficiently delicate 

 thermometric apparatus. Under the head of animal heat, 

 in another volume, we have given the results of recent ob- 



1 Du BOIS-REYMOND, loc. cit. 9 DONDERS, be. cit. 



