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APPENDIX 



with a pencil. Continue moving the pin head toward the black spot 

 and fix in the same manner the place of reappearance. of the head 

 of the pin. These two spots indicate the lateral extremities of the 

 blind spot. Its outline is to be determined by moving the pin head 

 toward it from various directions and fixing the point of disap- 

 pearance in each of them. 



The Field of Color Vision. Let one student of a pair look fixedly 

 with the right eye at a spot in an upright screen, supporting the 

 chin firmly. The other student moves a small square of colored 

 paper toward the "spot" from the margin of the screen. The 

 squares of paper should be fixed to straws or stiff wires so they 



FIG. 158. Diagrams illustrating Schemer's experiment. In A the eye is ac- 

 commodated for distant vision and rays from the pin P strike the retina before 

 they meet. The image through the right hand pin hole falls upon the right hand 

 side of the retina, just opposite to the usual manner. In B the rays cross before strik- 

 ing the retina. The relation of images to pin holes is therefore the same as in 

 ordinary vision. 



can be handled readily. Red, green, blue, yellow, and white should 

 be the colors provided. The subject should not know which color 

 is being used. As soon as he recognizes the color he should report 

 it, and the color should be marked on the screen. If the color is 

 incorrectly named, continue moving the square inward until it is 

 correctly perceived. Repeat the test along different meridians and 

 with different colors until the field of each color has been roughly 

 outlined. 



BLOOD 



Histological Structure. Blood is composed of a liquid, the plasma, 

 in which are several kinds of minute structures, the corpuscles, red 

 and colorless, and the platelets. 



A sample of blood for observation is prepared as follows: Provide 



