LESSON XXXVI 



THE SENSE ORGANS 



CUTANEOUS AND MUSCULAR SENSATIONS 



1. Histologic Examination of Tactile Corpuscles. Place different 

 tactile corpuscles under the low and high powers of a microscope and 

 study their structure. 



2. Touch Localization. Touch the skin of the hand of the subject 

 with the pointed end of a pencil, his eyes being kept closed throughout 

 this experiment. Let him then place the blunt end of a pencil upon 

 the area stimulated. Measure with a millimeter scale the error made 

 by him. Repeat the foregoing experiment upon the forearm and cheek 

 of the same subject. 



Touch the skin of the subject twice in quick succession, selecting 

 for the two stimulations either precisely the same point, or two points 

 lying close to one another. Let the subject state whether two areas 

 have been stimulated or only one. 



3. Touch Discrimination. By touching different areas of the sur- 

 face of the hand, arm, and face with the points of a caliper ascertain how 



FIG. 100. ESTHESIOMETER WITH GUARDED POINTS. (Stirling.) 



widely this instrument must be opened in order that its points may be 

 felt as two. Record in millimeters the results for each part stimulated, 

 and compare them, paying special attention to the relative sensitiveness 

 of the lips, cheeks, tongue, and the flexor and extensor surfaces of the 

 arm. In the latter case observe that the sensibility increases in the 

 direction of the fingers and also in the transverse direction rather than 

 along the longitudinal axis of the limb. 



4. Action of Cocain. Press the point of a needle upon the tongue 

 and note the degree of pressure necessary to produce a distinct sensa- 

 tion of pain. Touch this area with the end of a camel's-hair brush, 

 moistened with a 4 per cent, solution of cocain. What changes do 

 you note? 



5. Aristotle's Experiment. Cross the right middle and index-fingers 

 and place them upon the palmar surface of the left hand. Place a 

 small shot between them and roll it about in the palm of the hand. 

 Describe the sensation. 



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