i '"iiiKct the primary c>il through a sjmple kev in a dry cell. I )n 

 single make and break shocks evoke a reflex response? Me ver\ 

 careful in this ca-e t" di-tin^uish bet \\cen a direct stimulation of 

 llie muscle liy the eleciric current and a reflex stimulation from the 

 central nervous system. Stiinulale with regularly repeated iiva// 

 make and break -hnck^, and test \vhether under these circumstance^ 

 retlex action can result fr m the summation of afferent impulses. 

 I i" the -^timuli are repeated more rapidly, does the reflex occur 

 sooner? \\'hat is the effect of increasing the strength of the stimuli 

 and maintaining the -ame rate of stimulation? 



2\(). Inhibition. Use the fmg and a]>])aratus as described in 

 the foregoing experiment, hut arrange the inductorium to deliver 

 a tetanixing current. 



I'n vide a vessel of \vater. Immerse the toes of the right leg 

 nf the fmg in 0.5', stil])huric acid and note the time required 

 before retlex action occur-. Without any delay wash off the acid 

 in water. After an interval of 3 minutes, stimulate the left foot 

 with a weak tetanixing current a> the right is again immersed in 

 the acid. If the foot is not withdrawn from the acid after 20 

 seconds, st p the tetanizing currents. What has been the effect of 

 the afferent impulses frnm the left foot on the efferent imputes to 

 the right leg? After again washing the leg in water, prove that 

 the sensory endings in the skin are still irritable to the acid. 



^2(i. Irradiation. Use a tetanizing current and arrange as in 

 experiment Ji<). Start with a subminimal stimulus and then gradu- 

 ually increase its strength, determining the effect on the retlex 

 movement produced. I )oes the reflex become "crossed"? H es it 

 extend to anterior regions? Kecnrd the order nf spread with 

 increasing strengths of stimulus. 



_'_'!. Augmentation. Determine the ease with which the "knee 

 jerk" is -iven, Using your partner a- a subject. Let him then pull 

 upon his clasped hands in a maximum muscular eft'nrt and again 

 determine the activity of the "knee jerk". I> there any difference? 



222. Mmiifictitiiin nf rr//<M- response hy altcriin/ condition of 

 //. rrr-i -m//m/.v. I'rnductioii of hypersensitiveness of cntane >us 

 nerve-endings can be induced by s dium citrate. Suspend the frog 

 that the feel dip in in S Xa citrate solution. After mie to two 

 minutes withdraw the feet from the citrate solution and dip in 

 ordinary tap water. Note the effect. Kcplace in citrate solution. 

 Note the effect. 



\fter producing the -eiisjiivc condition as before, dip the Frog's 



