LABORATORY EXPERIMENTS ON THE SENSE ORGANS 



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a judgment of the size and distance of the former by comparison. Many 

 visual deceptions are based on these comparisons, a fact that is often taken 

 advantage of by photographers. It is also well known that people living in 

 a moist, hazy climate are utterly unable accurately to estimate distances 

 when suddenly transferred to a clear mountain climate. 



LABORATORY DIRECTIONS FOR EXPERIMENTS ON THE 

 SENSE ORGANS. 



i. Touch. Use the small compasses with rounded tips provided 

 for the purpose, and determine the power of localization of the sense of touch 

 as follows: Have the person observed close his eyes, then touch different 

 parts of the skin, of the hand, arm, face, neck, etc., and let the observed one 

 announce the exact point touched. 



The localization can also be determined by touching two points 6n the 

 skin with the points of the compasses separated by varying distances. Ex- 

 amine especially the skin on the forearm, on the back of the hand, on the 

 palm of the hand, the tips of the fingers, and at different points on the face, 

 including the lips and tip of the tongue. Touch these regions of the skin 



FIG. 480. Aristotle's Experiment. 



with either one or with two points of the compasses, and allow the person 

 observed to announce results, drawing your conclusions according to the 

 principle of trial and error. Make a table showing the power of local dis- 

 crimination in the different regions. 



2. Aristotle's Touch Experiment. Roll the tips of the middle and 

 index fingers over a marble and note that the sensation from the two fingers 

 is interpreted as that of a single object. Now cross the fingers and repeat 

 the experiment. This time there is the sensation of touching two spheres. 



3. Temperature Sensations. It is a common experience that the 

 hand brought in the neighborhood of a warm or a cold object develops the 



