CUTANEOUS AND INTERNAL SENSATIONS. 263 



The Temperature Senses. The main facts regarding the 

 distribution of heat and cold spots have been determined. In gen- 

 eral, the cold spots are more numerous than the warm spots, and 

 react more promptly to their adequate stimulus. The cold spots 

 or the cold sense may be present in places devoid of the sense of 

 warmth; thus, it is said that the glans penis possesses only the 

 cold sense. The threshold stimulus varies also in different parts 

 of the skin, the tip of the tongue requiring the smallest stimulus 

 to arouse a sensation, and the eyelids, forehead, cheeks, lips, limbs, 

 and trunk following in the order named. According to Goldscheider, 

 the spots on most portions of the skin form chains that have a some- 

 what radiate arrangement with reference to the hair follicles. The 

 temperature points possess each its adequate stimulus, that for the 

 cold spot being temperatures lower than the skin or of the terminal 

 organ of the cold nerves, that for the heat spots temperatures higher 

 than their own. Apparently, therefore, one end-organ is excited 

 by a diminution in the atomic movements of its organ, and the 

 other by an increase. Nothing is known, however, of the exact 

 nature of the stimulating process. From the standpoint of specific 

 nerve energies it is most interesting to find that these points, particu- 

 larly the cold spots, may be stimulated by other than their adequate 

 stimuli. Mechanical and electrical stimulation has in the hands of 

 several observers been efficient in causing a sensation of cold upon 

 a cold spot and of heat upon a warm spot. Some chemical stimuli 

 are also effective. Menthol applied to the skin gives a cold sensa- 

 tion, while, on the other hand, if the arm be plunged into a jar of 

 carbon-dioxid gas a distinct warm sensation will be experienced. 

 A curious effect of this kind is what is known as the paradoxical cold 

 reaction. It is produced by applying a very warm object, with a 

 temperature of 40 to 60 C., to a cold spot. In many cases this 

 spot is stimulated and a cold sensation is felt. The same result 

 may be felt at the instant of entering a hot bath. Many efforts 

 have been made to determine whether there is a specific kind of 

 end-organ for each of these senses. Numerous observers have 

 cut out the skin from cold or hot spots and examined the removed 

 part carefully by histological methods. The general result has been 

 that no distinctive end-organs have been found. Von Frey, how- 

 ever, believes that, although the heat spots are supplied simply 

 by a terminal end plexus, the cold spots in some places at least have 

 as a special end-organ the end-bulbs of Krause. This conclusion is 

 based upon the fact that these end-bulbs are found in places, such 

 as the glans penis and conjunctiva, where the cold sense is espe- 

 cially prominent or exclusively present. 



The Sense of Pressure. The pressure points are smaller and 

 more numerous than the cold or warm spots. Von Frey has shown 



