CUTANEOUS SENSATIONS. 301 



(<r/) The Vater-Pacini corpuscles, whose capsule is com- 

 posed of many concentric lamellae. 



2. Qualities of cutaneous sensations. There are four 

 qualities of cutaneous sensations, viz., touch, heat, cold, and 

 pain. 



These various qualities are located in various parts in the 

 skin. There are portions whose stimulation calls forth 

 tactile sensations only, so-called tactile or touch points; we 

 can also discriminate warmth, cold, and pain points. 



These four kinds of points are not evenly distributed over the 

 whole body. Some of them are lacking in certain regions of the 

 body, e.g. the central part of the cornea has only pain points, while 

 its peripheral portion is provided with pain and cold points. The 

 glans penis contains no tactile points ; a part of the mucous mem- 

 brane of the cheek lacks pain points. 



In those regions of the body where the four kinds cf points are all 

 found, the pain points are generally most numerous, then follow the 

 tactile and cold points, while the warm points are least numerous. 



(a) Tactile sensation. The adequate stimulus for the 

 tactile sense organs is the pressure exerted upon the skin. 

 Concerning the nature of the stimulation of nerve endings 

 "by pressure nothing is known. Stimulation by pressure 

 occurs only at the boundary of the portion of the skin 

 pressed, where, therefore, a fall in pressure exists. 



For example, if a finger is dipped in mercury, sensations of 

 pressure are not felt in the portion of the finger below the mercury, 

 but at the circle formed by the level of the mercury. 



Tactile sensations can also be produced by pulling the skin. If 

 the pull is exerted upon a very small area of the skin, for example 

 upon an individual tactile point, the sensation produced is nearly 

 like that produced by pressure. Only when a larger portion is 

 stimulated can we differentiate between pull and pressure. 



The organs for the tactile sensation are probably the nerve 

 wreaths of the hair [Haarnervenkranze] and the corpuscles 

 of Meissner, for the following reasons: 



i. In the regions of the body covered with hair, a tactile 

 point is found very near the exit of each hair. The hair 

 serves as a tactile apparatus, forming a lever whose shorter 

 arm is in contact with the sensory mechani^rtiT the^kjinT 

 while the longer arm receives the stimulj^^^ 



\ A R Y, 



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