6io 



THE NERVE CELL. 



the frog's cerebral hemisphere and the response of the leg muscles is 0-05 

 second. 1 Langendorff and Krawsoff- further found a difference of about 

 0-02 second between the lost time obtained on stimulating the cerebrum 

 and that obtained on stimulating the cut surface of the medulla oblongata. 

 This, therefore, represents in the frog the lost time of the cerebral cortex 

 itself. Almost the same figure (0*015 second to 0'02 second) was obtained for 

 the cortex of the dog by Francois-Franck and Pitres, 3 Bubnoff and Heiden- 

 hain, 4 and by JSTovi and Grandis. 5 Wilson 6 gives a closely corresponding 

 result for the latency of the optic lobes of the frog. 



The time of response (reaction time) by a voluntary movement 

 (usually of the hand) to a stimulus applied to one of the sense organs, 

 varies, as has been said, with different individuals and in the same 

 individual according to his physiological condition at the time. There 



$r.i 



Fig. 308. —Diagram to show the relative number of the synapses in the visual 

 and auditory organs. — G. Retzius. 



is, further, a notable difference between the reaction times for different 

 sense organs stimulated in the natural way. This is shown by the 

 following figures from Eichet, 7 which represent the mean results arrived 

 at by various authors : — 



Reaction Times. 



Source of Excitation. 

 Sudden sound 

 Electric flash 

 Touch on skin 



0*150 second. 

 0-195 „ 

 0-145 ,. 



1 Similar results have been got in the dog by Franck and Pitres (Francois-Franck, 

 "Lecons," 1887) and others, and in the monkey by myself [Internal. Monatschr. f. Anat. 

 u. Physiol., Leipzig, 1888, Bd. v.). 



2 Arch./. Physiol., Leipzig, 1879, S. 90. 



3 Trav.'dula'b. da Marc y, 1878-9, p. 413. 



4 Arch. f. d. gcs. Physiol., Bonn, 188], Bd. xxvi. 



5 Riv. sper, difreniat., Reggio-Emilia, 1888, tome xiii. 



6 Journ. Physiol., Cambridge and London, 1890, vol. xi. p. 504. 



7 " Dictionuaire de physiologie," Paris, tome iii. p. 19. 



