feet into m-cane-sugar-solution. Note the effect. What is the 

 general physiological effect of such a solution ? Then dip the feet 

 into the water as before. Is there any response? 



Can the hypersensitive condition he restored by the citrate solu- 

 tion? i. e., are these changes of sensitivity reversible? 



223. Modification of rcflc.r by altering condition of cord. Ef- 

 fect of strychnine on rcflc.v action. Inject with a fine-pointed pipette 

 a few drops of 0.5^ solution of strychnine sulphate into the dorsal 

 lymph sac of a frog whose brain has been destroyed. After a few 

 minutes test the reflex excitability of the animal by touching the 

 foot with a needle. Note carefully the character of the response 

 and how it differs from that of an unstrychninized frog. Note 

 evidence that as the influence of the strychnine becomes more 

 marked the afferent impulses spread more and more readily through- 

 cut the entire cord. Then destroy the spinal cord and stimulate the 

 animal as before. What is the essential nature of the change pro- 

 duced in the cord by strychnine? 



224. Production of hyper-irritability of the ucrrc-trnnk. 

 Under some conditions the nerve-trunks become abnormally sensi- 

 tive, and a reflex response may be modified by this cause. Hyper- 

 sensitiveness to contact may be induced as follows : Immerse the 

 nerve of a nerve-muscle preparation in m/8 Na citrate solution for 

 about 5 minutes. (Let the muscle rest on moist filter paper on a 

 glass plate from the edge of which the nerve hangs down into the 

 beaker containing the solution.) Is there any effect on the muscle 

 while the nerve remains in the solution ? Then remove the nerve 

 from the solution and let it hang in the air. Any effect? Touch 

 it with a glass rod or the handle of a scalpel. What is the result? 

 Dip the nerve in Ringer's solution for a short time and again test its 

 contact reaction. Can the hypersensitiveness be produced a second 

 time? Muscle may be similarly rendered hypersensitive. 



225. Reaction time. Place a signal magnet in circuit with two 

 simple keys and the primary of an inductorium arranged for single 

 shocks. The signal magnet is arranged to write on a drum (turned 

 by hand ) just above a vibrating tuning fork. One student is to place 

 the stimulating electrodes from the secondary terminals of the induc- 

 torium on his tongue and his right hand on one of the keys which 

 must be closed. He should close his eyes and concentrate attention 

 on the stimulation of his tongue. When stimulated he should 

 instantly open the key in his right hand. The other student must 

 start the tuning fork, rotate the drum and close the second key 



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