REFLEX MOVEMENTS IN MAMMALS. ' 241 



must be used, the exact relationship of the signal pointer to the 

 recording lever being indicated by alignment marks (see p. 94). 

 A time tracing, preferably of 1/100 sec. must also be taken. Several 

 observations on the flexion reflex with stimuli of varying strength 

 will show the latent period to vary from about 0.03 to 0.12 sec. 

 The latent time of the jerk is much shorter. (The signal for the 

 application of the stimulus is afforded in this case by the slight 

 movement of the lever produced by the blow to the tendon, the 

 attachment of the threads to the levers being adjusted so as to make 

 them sensitive enough to record this). 



The latent period of the scratch reflex (using the stigmatic 

 electrode) is relatively very long and it varies with the strength of 

 the stimulus. Taking these results with those already attained 

 on the palpebral reflex (p. 104) into consideration, what con- 

 clusions do you draw concerning the latency of reflex action in 

 general? What corrections must be made to determine the true 

 or reduced reflex time? 



2. GRADING OF INTENSITY. This is investigated for the flexion 

 and scratch reflexes by varying the strength of the electrical stimu- 

 lus and for the extensor thrust by applying varying degrees of 

 pressure to the paws. How do the results obtained from these two 

 types of reflex compare with those already obtained for the palpe- 

 bral reflex? 



3. SUMMATION. Using the flexion reflex, a strength of current 

 is found which is just ineffectual when single shocks are applied, 

 a simple tapping key being inserted in the primary circuit of the 

 inductorium in place of the vibrating hammer. The shocks are then 

 applied frequently. Is the summation more pronounced than you 

 found it to be for isolated nerve ? 



4. AFTER EFFECT. By recording the movement of the flexion 

 reflex on a fairly rapid drum, the degree of after effect in relation- 

 ship to the strength of stimulus is observed. Both single shocks 

 and tetanizing shocks are employed. hi what respects do the 

 results differ from those obtained on a nerve? 



5. REFLEX FATIGUE. The effect of maintained stimulation is 

 studied in the flexion and scratch reflexes, using a slow drum. How 

 does reflex fatigue differ from fatigue in an isolated nerve-muscle 

 preparation? After the leg has been thoroughly fatigued for the 



