ACTION OF AMYL NITRITE 401 



shadows of the corpuscles circulating in the capillaries of 

 the retina in front of the rods and cones. Observe carefully 

 (but do not try to fix the eye on any given point) about how 

 numerous these objects are in the field of vision. If the 

 number were suddenly doubled or reduced by half, could 

 you detect the difference ! Do not strain your eyes in watch- 

 ing for the objects as efforts in this direction will avail 

 nothing and may even appear to decrease the number of 

 shadows visible. Can you make out the shape of individual 

 corpuscles f Do the shadows appear to move in set paths, 

 i.e., within the lumen of the capillaries! Do any two or 

 more shadows follow the same course as near as you can 

 judge ? When the student has learned the appearance of 

 these shadows well and can readily estimate any consider- 

 able change in their number then, as the subject keeps 

 watching the shadows, an amyl nitrite pearl is broken near 

 his nose and he quickly breathes in its vapors. Watch his 

 respiratory movements closely. Does his face flush? The 

 subject should not know what change to expect in the num- 

 ber or movement of the corpuscle shadows seen by him, 

 In what ways may amyl nitrite influence the appearance of 

 these shadows? Explain in detail. 



EXPERIMENT CXXI. 



Amyl Nitrite. (Student: Retinal Blood Vessels.) 



1. Through the center of a stiff, opaque card (calling 

 card, or smoked, varnished drum paper) a pin hole is 

 made. The card may be about two by three inches in size. 

 The subject sits down at perfect rest in front of a window 

 through which he can see a considerable expanse of clear, 

 blue sky. A few objects, as the top of a building or a tree, 

 may well be located about 200 to 400 feet in front of the 

 window, so the subject by lowering his field of vision a little 

 can sec the upper part of these objects. The purpose of 



