TACTILE SENSE. 



731 



areas are found little fields which are insensitive and which are rela- 

 tively much larger than the sensitive areas, or "spots." It has been 

 demonstrated that each "spot" has its own specific function to per- 

 form, whether that be touch, cold, warmth, or pain. Each little 

 sensitive area no doubt marks the site of single or groups of sensory 

 corpuscles, end-organs, or bulbs, of the terminations of various 

 nerves. Where the nerves terminate, there are the sense-spots rep- 

 resented upon the skin's surface. 



Some one has very aptly likened the skin with its sense-spots 

 to a pond upon whose surface, as well as just below the same, are 

 seen lily leaves floating. The leaves represent the sense-spots. A 

 pebble thrown into the pond may strike one or more leaves, depend- 



Tz 



Tsch 



Fig. 299. Transverse Section of Two Grandry's Corpuscles from the 

 Tongue of a Duck. X 450. ( SOBOTTA. ) 



One of the corpuscles shows two, and the other, four tactile cells, mn, 

 Medullated nerve-fibers, entering the corpuscle. Tsch, Tactile discs. Tz, Tactile 

 cells. 



ing upon how close together they are growing. The pebble repre- 

 sents a stimulus, and by its presence temporarily stirs up or throws 

 into a state of excitation the leaves struck as well as some of those 

 adjacent. 



Upon the skin's surface may be demonstrated "touch-spots/' 

 "cold-spots," "warmth-spots," and "pain-spots." These are all mixed 

 up, though those of one kind may be more strongly in evidence in 

 certain areas. As a rule, "pain-spots" are found to be the most 

 numerous: "warmth-spots" -are the least likely to be found. 



SOLIDS. These act upon the sense of touch either by pressure 

 or by traction. Pressure may be from zero to a maximum whose 

 limit is the disorganization of the tissues. Up to a certain minimum, 

 which depends upon the sensibility of the region, the application of 

 pressure excites no sensation. The minimum pressure corresponds 

 to the sensation of simple contact; this by degrees gives way to the 



