THE CENTRAL NERVOUS SYSTEM 385 



Reflex actions may be inhibited by the simul- 

 taneous stimulation of sensory nerves. 



Through Central Afferent Paths ; the Optic 

 Lobes. 1. Expose the brain according to the 

 directions already given (page 377). Immediately 

 posterior to the cerebral hemispheres lie the optic 

 lobes, two gray spherical bodies. Separate the 

 cerebral hemispheres from the optic lobes by a 

 transverse incision, and carefully remove the 

 hemispheres. Wait until the shock of the opera- 

 tion has passed. Now suspend the frog so that 

 the tips of the toes hang above a shallow dish 

 containing water made strongly sour to the taste 

 with dilute sulphuric acid. Determine the reflex 

 time. Wash off the acid and, after a moment's 

 rest, sprinkle a very little finely powdered com- 

 mon salt on the cut surface of the optic lobes. 

 Again determine the reflex time. 



The reflex time will be found to be markedly 

 incr 'ased by the stimulation of the optic lobes. 



2. Prepare a second frog in the same manner. 

 Determine the reflex time. Now instead of stim- 

 ulating the optic lobes, remove them, and again 

 determine the reflex time. 



The removal of the optic lobes shortens the 

 reflex time. 



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