CHAPTER XXIV. 



SKIN SENSATIONS. TASTE 



There are three types of skin sensations, the appreciation of 

 differences of temperature (temperature sense), the sense of touch, 

 and the sense of pain. Since our knowledge of the normal behaviour 

 of each of these senses depends on subjective phenomena, each 

 student must perform the fundamental experiments as given below, 

 both on himself and on others, and must accurately describe the 

 results in his notes. 



TEMPERATURE SENSE. 



It is the rate at which heat is being gained or lost by the skin, 

 and not the actual degree of temperature of the applied object, 

 that is determined by our sensations. 



Experiment 78. Place a finger of one hand in water at 2 C. 

 and the corresponding finger of the other hand in water at 40 C. 

 After no temperature sensations are felt by either finger, transfer 

 them simultaneously at 30 C. Note the nature of resulting 

 temperature sensations in the two fingers. 



The temperature sensations are received by "hot" and "cold" 

 spots scattered over the skin, the cold spots being the more numer- 

 ous (Fig. 59). 



Experiment 79. Mark out an area of skin on the back of the 

 hand, say 20 X20 mm. square. The hand should be resting com- 

 fortably on a table and the subject blindfolded. With a thermo- 

 aesthesiometer (a test tube drawn out to a point will serve the 

 purpose), containing water at 40 C., proceed to explore the 

 selected area, systematically, in parallel lines, marking with ink 

 the spots at which a distinct sensation of warmth is experienced. 

 When all the area has been explored accurately, transfer the 

 spots to ruled paper, and with the aesthesiometer containing 

 water at a temperature of 15 C., proceed in the same way to 

 determine the cold spots. Note that the cold spots, besides 



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