Vol. XLII. May, 1922. No. 5 



BIOLOGICAL BULLETIN 



RETINAL REFLEXES OF NARCOTIZED ANIMALS TO 



SUDDEN CHANGES OF INTENSITY OF 



ILLUMINATION. 



A. T. CAMERON AND C. H. O'DONOGHUE. 

 (From the Marine Biological Station, Nanaimo, B. C., Canada.) 



In March last, Cameron and Sedziak, working in Winnipeg, 

 published a note 1 describing a peculiar reaction of the frog (R. 

 pipicns from Illinois), narcotized with benzene, to sudden changes 

 of illumination, a reaction noted incidentally in rehearsing a class 

 experiment on the relative pharmacological effects of different 

 hydrocarbons. 



' Injection of 0.5 c.c. of pure benzene into the anterior lymph 

 sac of a frog weighing about fifty grams produces distinct effects 

 within a few minutes. The eyes close, movements become slug- 

 gish, when turned over the animal recovers its normal position with 

 difficulty, and in most cases can no longer do so after ten minutes. 

 The body often becomes characteristically arched. The usual re- 

 flexes gradually disappear. Breathing ceases. With the gradual 

 disappearance of the conjunctival reflex the eye opens, the nictitat- 

 ing membrane is usually drawn down, and the ' retinal ' reflex can 

 be observed. Initially it would appear to be evoked by any rapid 

 change in intensity of illumination. When the hand is passed sud- 

 denly between the frog's eye and the source of light, within one 

 or two seconds the head is moved, and usually the hind limbs also. 

 When a bright light (electric light at a distance of one foot) is 

 suddenly switched on, the response follows. On switching the 

 light off the response is more marked. Direction of light to and 

 from the pupil only, the rest of the head being screened from light 

 changes, evokes the response. Gradually the response to sudden 

 increase of illumination ceases. The response to sudden decrease 



217 



