CUTANEOUS AND INTERNAL SENSATIONS. 283 



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 

 of termination serving as an end-organ. On account of their 

 position they are stimulated by any pressure exerted upon 

 the hair. The hair, indeed, acts like a lever and transmits any pres- 

 sure applied to it with increased intensity, acting, therefore, as re- 

 gards the pressure organ somewhat like the ear-bones in the case 

 of the endings of the auditory nerve. In parts of the body not 

 furnished with hairs the tactile or Meissner corpuscles are found 

 and these structures doubtless function as pressure end-organs. 

 They are particularly abundant in the parts of the hand and feet in 

 which a delicate sense of pressure is present in spite of a much thick- 

 ened epidermis. It has been estimated that for the entire surface 

 of the body, excluding the head region, there are about 500,000 

 of these pressure points. These points are close together on those 

 parts, such as the tongue and fingers, which have a delicate tactile 

 sense and more widely scattered where the sense is less developed. 



The Threshold Stimulus and the Localizing Power. The 



