112 ' Gunn 



At 9.0 when pinched he went into a convulsion, in which the hind Kmbs 

 were rigidly extended with slight opisthotonus, followed by emprosthotonus, 

 with the body flexed and the arms flexed under it. The fly-catching reflex 

 was elicited as before. 



At 7.20 a.m. next morning he still had when pinched convulsions 

 similar to that described. The eyes were fully open. If a bright object 

 was held near his eyes, he snapped at it, extending his tongue. He could 

 not turn over when placed on his back. 



During all this day he remained in nearly the same condition, with, 

 however, some increase of co-ordinating power, for by the end of the day he 

 could turn over, though still with some difllculty, when laid on his back. 



On the second day after injection he sat with his limbs fully drawn 

 up, made frequent spontaneous movements, could jump well, and turned 

 over rapidly when laid on his back. When his hand or nose was touched 

 he no longer snapped, and when a bright object was held near his eyes he 

 moved away as a normal frog does. He appeared to have practically com- 

 pletely recovered, except that his respirations were only ten per ten seconds. 

 Two days later, however, the rate of the respirations was the same as 

 before injection. 



When the earlier symptoms are analysed with a view to their explana- 

 tion, it is apparent that the cessation of voluntary movements, the inco- 

 ordination of movement when such movement is elicited by stimulation, 

 and the loss of the power of jumping are symptoms which so much resemble 

 those which result from operative destruction of the cerebrum, mid-brain 

 and cerebellum as to lead one to infer that yohimbine early in its action 

 abolishes the functions of these parts. 



That the medulla oblongata, too, is involved is shown by the cessation 

 of respiration, and by the inability of the animal to recover its normal 

 posture when laid on its back. These eflfects are not the result of a peri- 

 pheral paralysis, for, as I have ascertained from control experiments, the 

 motor nerves and the voluntary muscles at this time react normally to 

 electrical stimulation. 



Since pinching the foot elicits withdrawal of the leg as promptly as 

 before injection, yohimbine does not impair the functions of the spinal cord 

 as it does those of the higher parts of the central nervous system. 



Is there anything in the nature of the action of yohimbine on the central 

 nervous system to explain the appearance of the " fly-catching reflex " ? 



In every one of a large number of experiments with doses of yohimbine 

 lactate ranging from 0*22 gm. to 0-08 gm. per kilo subcutaneously, I have 

 found this reflex elicitable at some time during the experiment. With the 

 largest of these doses (0-08 gm. per kilo), which killed the frog in one 

 and a half hours, it was obtained only once, namely, about an hour after 

 injection, though it was tested for at regular intervals of a few minutes. 

 With the smallest of these doses this reflex could be elicited for over 

 twenty-four hours. 



