368 



THE SENSES 



however, is their liminal intensity for electrical stimuli, which is lower 

 than that of touch. 



The afferent nerves of these spots are unknown. There is much evi- 

 dence, physiological and pathological, that the impulses pass up the gray 

 matter of the cord for a longer or shorter distance, perhaps only passing 

 obliquely through it or across it. As for the center of pain, Budge 

 found evidence in animals of pain from stimulation of the corpora quadri- 

 gemina, hut this evidence is inconclusive. Many things go to show 

 that a center is stimulatable with a normal result only by the stimulus 

 coming from its own end-organ, and the pain-stimulus we do not know 

 how to imitate. Cases of analgesia (abolition of the pain-sense) are in 



FIG. 220 



A genital sense-organ from the glans penis of a man: a, sheath about the nervelet; 6, con- 

 nective-tissue sheath of the corpuscle; c, nerve-fibers which ramify inside the end-organ. If 

 the body may be said to have afferent organs of a pleasure-sense, this is probably one of them. 

 (Dogiel.) 



themselves alone strong evidence that a neural mechanism of pain is 

 part of the nervous system. It is hard to think how an abnormality 

 could arise which would throw out of action only one set of experiences 

 unless the nerve-arrangements for that set of sense-impressions were 

 distinct in some way. Cases of various sorts and degrees of analgesia 

 are common and similar to the sensory paralysis of other sets of nerves 

 much better known in their courses and endings. 



Besides the pain-spots of the skin, some of the mucosse and viscera, 

 notably the heart, the serous coverings, and muscle obviously have pain- 

 organs as a part of their complete mechanism. 



