REFLEX ACTION : REACTION TIME : EXCITATION OF CORTEX 97 



Time of reflex response ; Turek's method. Having allowed the 

 frog to become quiescent, allow the extremity of the toes to dip into 

 a small beaker of dilute sulphuric acid (2 per 1000). Count the time 

 in half-seconds which elapses between the application of the acid and 

 the withdrawal of the toe. Wash the acid off immediately after the 

 withdrawal. Kepeat this observation three times at intervals of a 

 few minutes ; calculate and record the average time of response. 



Inhibition of reflex by an accompanying excitation ; Setschenow's 

 experiment. Place a crystal of chloride of sodium upon the optic 

 lobes (or on the upper cut end of the cord if the whole brain have been 

 removed), and again determine the time of response after application 

 of the dilute sulphuric acid to the toes. 



Reflex inhibition of heart. Fix the frog securely on its back upon 

 the frog-cork ; expose the heart sufficiently for its beats to be ob- 

 served. Tap the abdomen smartly with some small heavy instrument 

 such as a metal rod or the handle of a knife. The effect will be to 

 produce a slowing or complete stoppage of the heart, which will, how- 

 ever, soon recommence beating. The same result is obtained if the 

 abdomen be opened and a loop of intestine strongly stimulated. 



For this experiment the medulla oblongata must be left. 



Effect of strychnine on reflex action. Inject a very small dose 

 of strychnine nitrate (1 drop of a 1 per 1000 solution) under the skin 

 of a decerebrate frog, and wait for a few minutes until it is absorbed 

 into and distributed by the circulation. It will be found that pinching 

 the skin eventually produces not simple purposeful reflex actions, 

 but convulsive contractions of all the muscles in the body. 



Tendon reflex ; knee jerk. In a subject seated in a chair with 

 one leg crossed over the other, or seated on a table with the legs 

 dangling, strike the patellar tendon with the handle of a knife or 

 the back of a thin book. Notice the sudden jerk forward of the 

 leg owing to the contraction of the vastus internus. This can be 

 recorded by a transmission myograph (see p. 38). 



Reinforcement of tendon reflex. Just before striking the patellar 

 tendon cause the subject to clench his fist. The movement of the 

 leg will be stronger, or will be elicited with a slighter tap on the 

 tendon. 



Reflex action in mammals. The reflex actions which depend upon the spinal 

 cord can be studied in a Sherrington preparation (see p. 81), reflexes being 

 elicited in various ways, as by pinching or pricking one of the paws or the skin 

 of the flank or side of the thorax. Tendon-reflexes, such as the knee jerk (see 

 above) and the ankle-clonus, obtained by forcibly bending the foot at the 

 ankle, can also be well observed in such a preparation. 



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