242 EXPERIMENTAL PHYSIOLOGY. 



flexion reflex, the scratch reflex is elicitated by mechanical and 

 electrical stimuli. What do the results indicate as to the locus of 

 fatigue in the reflex arc? 



6. IMMEDIATE INDUCTION. The end of the handle of a scalpel 

 or of a small ruler is pressed against the skin of a scratch area, but 

 there is no response. If the same object be moved on the skin, 

 however, the scratch movement is likely to be set up. What is the 

 explanation of the result? What is the analagous experiment on 

 vision? 



7. SUCCESSIVE INDUCTION. Using a slow drum, record a con- 

 siderable number of knee jerks produced by regularly applied taps 

 of as nearly as possible equal intensity to the patellar tendon, and 

 when there is approximate equality in the heights of the contrac- 

 tions throw the corresponding leg for a few seconds into the flexion 

 reflex, meanwhile continuing the patellar taps. When the flexion 

 reflex subsides the tendon jerks are greatly exaggerated. Explain 

 why this shows successive induction. Demonstrate the same 

 phenomenon for the flexion reflex and extensor thrust, and for the 

 crossed extension reflex and flexion reflex. What is the analagous 

 experiment on vision? 



