CUTANEOUS AND INTERNAL SENSATIONS. 279 



smallest stimulus to arouse a sensation, and the eyelids, fore- 

 head, 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 somewhat radiate arrange- 

 ment 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. From the standpoint of specific nerve ener- 

 gies it is most interesting to find that these points, particularly 

 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. According to 

 Head and Rivers this reaction is rather characteristic of the 

 protopathic temperature fibers. It can be obtained, for example, 

 from the glans penis, which possesses only protopathic sensibility, 

 or during the course of regeneration of a severed cutaneous 

 nerve. In this latter condition hot objects applied to a cold 

 spot give a vivid sensation of cold. The same result may be 

 felt sometimes 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, however, 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 con- 

 junctiva, where the cold sense is especially prominent or exclu- 

 sively present. 



The (Epicritic) Sense of Pressure or Touch. — The cutaneous 

 pressure points are smaller and more numerous than the cold 

 or warm spots. Von Frey has shown that in those portions 

 of the body that are supplied with hairs the pressure points 

 lie over the hair follicles. The pressure nerve-fibers, in fact, 

 terminate in a ring surrounding the hair follicle, this form 



