ACTION OF AMYL NITRITE 403 



When the subject lias learned to recognize clearly the 

 size and appearance of these retinal vessel shadows he may 

 determine the action of anryl nitrite on them. He should 

 sit (or lie) at perfect ease, and his right hand should be 

 free to keep up the circular movement of the card. While 

 the card is moving and the vessels are being closely ob- 

 served an amyl nitrite pearl is broken near the subject's 

 nose and the vapors are rapidly inhaled. The subject 

 watches carefully for any change in the size or distribu- 

 tion (extension toward the macula or withdrawal there- 

 from) of the retinal vessel. How may amyl nitrite affect 

 these vessels? Explain in detail. 



EXPERIMENT CXXII. 

 Amyl Nitrite. (Student: Effect on Vision.) 



1. On the white, glazed surface of a sheet of drum paper 

 make a circular spot one-fourth inch in diameter with black 

 India ink. Behind the drum paper place several sheets of 

 perfectly white writing paper (or a sheet of white card- 

 board) to give a perfectly white background to the drum 

 paper. The subject now sits quietly and looks at the black 

 spot while amyl nitrite vapors are administered to him. 

 Around the black spot the subject watches for rings of dif- 

 ferent colors to appear. If these are observed how many 

 are there, what is their arrangement, and what colors are 

 seen? How long do they last? How does amyl nitrite act 

 to produce this effect ? What is the embryological origin of 

 the retina? 



If time permits it will be instructive to make a white spot 

 on a black background and repeat the experiment by inhal- 

 ing amyl nitrite vapors while looking intently at the white 

 spot. Do you know of any other drugs which will affect 

 color vision? On what nervous structures may such drugs 

 act? What relation does the retina bear to the cerebral 

 cortex ? 



