LABORATORY MANUAL OF PHYSIOLOGY. 



to regulate the distance of the subject's eyes from the point of fixa- 

 tion. The subject, with one eye screened, places himself directly 

 in front of the point of fixation and twenty centimetres from it. 

 Make a test object out of a piece of white paper, one centimetre 



FIG. 47. Use of Ophthalmoscope. Indirect method. S, eye of subject; , eye of 

 observer; M, mirror; L, source of light; C, convex lens; /, image of fundus. 



square, and affix it to a black handle. Let the operator move the 

 test object along one meridian, say the horizontal, from the pe- 

 riphery toward the point of fixation. As soon as the subject sees 

 the test object, make a chalk mark on the meridian, denoting the 

 place where it is first seen. In like manner go over at least eight 

 of the meridians. Join the points so obtained with a line, and the 

 result is the approximate field for white. 



In the same manner map out the field for blue and red. 



Which field is the largest, that for white, for blue, or for red? 

 Which is the smallest? 



DRUGS ACTING LOCALLY ON THE EYE. 



Those acting directly upon the eye are divided into (i) mydri- 

 atics (dilators of the pupil), such as atropine, homatropine, cocaine, 

 scopolamine, etc. 



(2) Myotics (pupil contractors), such as eserine and pilo- 

 carpine. 



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