THE EYE AMYL XITRITE 397 



crystalline lens belong? How is the eye focused for vary- 

 ing distances? What part does the lens play in this proc- 

 ess? Make two diagrams to show these actions. AYhat 

 drugs may influence these processes and how do the drugs 

 act? 



Examine the iris. Locate the anterior and posterior 

 chambers. AYith what is each filled ? May drugs influence 

 these chambers in any way ! If so how ? Can you find any 

 evidence of the existence of dilator muscle fibers for the 

 pupil? Where would you look for these? What is the in- 

 nervation of this set of fillers? What drugs act on the 

 dilator mechanism and where and how do these drugs act ? 

 How is the intraocular pressure controlled ? How may 

 drugs influence this? Can you find the sphincter muscle of 

 the iris ? How is this muscle innervated ? What part does 

 it play in accommodation? AVhat drugs may affect this 

 muscle and how and where do they act ? Compare the iris 

 of a bird with that of a mammal as regards the action of 

 atropine, pilocarpine and cocaine. Make a diagram show- 

 ing the structure and innervation of the eye and indicate 

 thereon with ledger lines the points where all drugs which 

 affect the eye and with which you are familiar act. Indi- 

 cate the nature of these actions with a plus ( + ) sign for 

 stimulation and a minus (--) sign for depression and paral- 

 ysis. Describe all nervous paths and elements involved in 

 the pupillary light reflex. AVhat is an Argyll-Robertson 

 pupil ? 



EXPERIMENT CXVIII. 



Amyl Nitrite. (Student: Plethysmographic Record, 



General Action.) 



1. Arrange your apparatus for taking a volume record 

 of the arm as shown in Fig. 326. AVhen all adjustments are 

 made fold a handkerchief over a three (or five) minim amyi 

 nitrite pearl and prepare to break the pearl by squeezing 



