160 



Mr. Graham Brown. 



possible that the reaction was a reflex in connection with the optical 

 mechanism. 



In several experiments it was found that unipolar stimulation applied to a 

 certain area on the ventral surface of the exposed fourth ventricle evoked 



Fig. 6.— Experiment M, XXV, record 315, 8481 ; 1.4:13.— Macacus rhesus. All the 

 dorsal spinal roots of the left (recording) fore limb divided in May, 1912. A record 

 of the reactions from the ipsilateral area on the cross-section of the mid-brain and 

 of the reactions from the contralateral crus cerebri obtained 1 hour and 8 minutes 

 after decerebration. 



The first reaction (O-P, ordinates o, o'-p, p') is that from the contralateral crus 

 cerebri (A). It demonstrates the typical " climbing " form of the contraction, and 

 the sudden relaxation on withdrawal of the exciting stimulus. [It was not possible 

 to induce an after-discharge by repeated stimuli in series.] 



In the second reaction an ipsilateral " dorsal focal point " stimulus is applied, and 

 gives the usual flexion followed by flexor after-discharge in this experiment that 

 would last for several minutes if undisturbed. 



In the third reaction (B) the crus stimulus is repeated during this after-discharge. 

 It gives first a slight relaxation, and then an augmentation of flexor contraction. 

 But, nevertheless, on withdrawal of the crus stimulus the sudden relaxation occurs 

 as in the " pure " crus reaction. The flexor after-discharge is abolished. 



