CH. XLVII.] 



TENDON REFLEXES. 



66 3 



2. The phenomena depend for their occurrence on the integrity 

 of the reflex arc. Disease or injury to the afferent nerve, efferent 

 nerve, or spinal grey matter, abolishes them. Thus they cannot 



fig. 490. The Knee-jerk. (Sowers.) 



be obtained in locomotor ataxy (damage to the posterior nerve- 

 roots), or in infantile paralysis (damage to the anterior horns of 

 grey matter). 



Fif?. 491. Ankle-clonus. (Gowen.) 



3. They are excessive in those conditions that increase the true 

 reflex irritability, such as severance of brain from cord, and in 

 lateral sclerosis. 



How, then, is it possible to reconcile these two sets of facts ? 



