THE " FLY-CATCHING REFLEX " IN THE FROG. By J. A. Gunn. 

 (From the Pharmacology Department, University of Edinburgh.) 



(Received for puhlicatioti l\th February 1908.) 



One of the most conspicuous symptoms which result in the frog from the 

 administration of toxic doses of yohimbine is the appearance of a fly- 

 catching reflex. This symptom is interesting not only on account of the 

 invariability of its occurrence, but also because it seems to illustrate the 

 close resemblance which may obtain between the effects of toxic action 

 and operative lesion on the central nervous system. 



The following experiment will serve to show the general effects produced 

 by a large sublethal dose of yohimbine in frogs, and also the relation which 

 the symptom under consideration bears to other symptoms. 



A healthy male frog (R. temporaria) weighing 29 grammes was used. 



At 3.7 p.m. the throat respirations were 30 in 10 seconds, the heart-beats 

 8 in 10 seconds. 



At 3.20, 0"7 cc. of a solution of yohimbine lactate (0"01 gm. in 5 cc.) was 

 injected into the dorsal lymph sac. This was equal to 0*048 gm. per kilo, 

 the minimum lethal dose being 0*05 gm. per kilo. 



At 3.35 the normal respirations had entirely ceased, and were replaced 

 by infrequent gulping movements. The head was lowered and the limbs 

 not fully drawn up. The frog made no spontaneous movements, but when 

 pinched jumped well, and when laid on his back recovered his usual posture 

 quickly. The conjunctival and limb reflexes were acute. The lower eyelid 

 covered half the eye. At 3.55 if pinched he did not jump, but moved 

 forward on his abdomen by kicking. When laid on his back he recovered 

 once, but when placed on his back a second time immediately after he was 

 unable to do so. 



At 4.15 when laid on his back he kicked vigorously, but coukl not 

 turn over. 



At 4.53 (one hour thirty-tliree minutes after injection) when laid on his 

 back he made a few feeble movements and then lay still with legs ex- 

 tended. When a foot was now pinched the leg was drawn up quickly. 

 Movements of any nature brought on fatigue very soon. When the 

 animal's hand or nose was touched he snapped in tlic direction touched, 

 extending his tongue as a frog does when catching a fly. 



At 7.0 he jumped feebly when pinched. Tliough in jumping he could 

 raise himself off the ground, his movements were badly co-ordinated ; for 

 example, one hind limb would get flexed behind the other. 



VOL. I. — APRIL 1908. 8 



