74 PRACTICAL PHYSIOLOGY 



Next place a crystal of chloride of sodium upon 

 the optic lobes, and again determine the time of 

 response after application of the dilute sulphuric 

 acid to the toes. It will probably be found to be 

 decidedly longer (inhibition of reflex by descending 

 excitation ; Setschenows experiment}. 



5. Lay the frog upon the frog-cork ; open the 

 abdomen and draw out a loop of intestine ; the 

 heart is also to be sufficiently exposed for its beats 

 to be observed. Now excite the intestine strongly, 

 either by induction shocks or mechanically by a 

 pinch or blow. The effect will be to produce a 

 slowing or complete stoppage of the heart, which 

 will, however, soon recommence beating (reflex in- 

 hibition of heart). 



6. Inject a very small dose of strychnin (i drop 

 of a i per 1,000 solution) under the skin of a 

 decerebrate frog, and wait for a few minutes until 

 it is absorbed into and distributed by the circula- 

 tion. It will then be found that the slightest touch 

 of the skin produces not a simple purposeful reflex 

 action, but convulsive contractions of all the mus- 

 cles in the body. 



Reaction time in man. The reaction time in 

 man may be determined by an arrangement of 

 electric signals, but is done more simply by Wal- 

 ler's apparatus. This consists of two wooden lev- 

 ers lying across a piece of india-rubber tube, 

 one end of which is closed, the other being con- 

 nected with a tambour which writes upon a drum, 

 the speed of which should be moderate. A screen 

 is used to hide the movements of the experimenter 



