REFLEX ACTION: REACTION TIME 113 



body, and the abdomen, always washing the acid away after each 

 observation. 



Time of reflex response ; Tiirck'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 1,000). Count the time 

 in seconds which elapses between the application of the acid and 

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

 withdrawal. Repeat this observation three times at intervals of a 

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



Inhibition of reflex ; Setschenow's experiment. Place a crystal of 

 salt upon the optic lobes (or on the upper cut end of the cord if the 

 whole brain has been removed), and again determine the time of 

 response after application of dilute sulphuric acid to the toes. 



Reflex inhibition of heart. Fix a decerebrate frog securely on its 

 back upon the frog-cork ; expose the heart sufficiently for its beats to 

 be observed. Tap the abdomen smartly with some small heavy 

 instrument, such as the handle of a pocket-knife. The effect will be 

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

 however, soon recommence beating. The same result is obtained if 

 the abdomen is opened and a loop of intestine strongly stimulated 

 by faradisation. 



For this experiment the medulla oblongata must be left. 



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

 of strychnine nitrate .(I drop of a 1 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 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. 39). 



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. 89), 

 reflexes being elicited in various ways, as by touching or pricking an 

 ear or a paw or the skin of the flank or the side of the thorax. 

 Tendon-reflexes, such as the knee-jerk (see above) and the ankle-clonus, 

 8 



