43° THE POPULAR SCIENCE MONTHLY 



justly described as stabbing, aching, burning, it owes its individual 

 character to the form of its onset and to its duration, and these in 

 turn depend upon either the vascular condition of the part affected — 

 the pumping of blood through the vessels of a tissue free to expand, or 

 packed in a bony case — or they are due to the effect upon the inflamed 

 or injured part of muscular contractions. If the injured part be inac- 

 cessible, pain has no " local sign." If it be on or near the surface of 

 the body the pain felt in it has or seems to have a topographical mean- 

 ing; but it is very doubtful whether the mind can localize the source 

 of pain in the absence of evidence simultaneously afforded by the 

 nervous apparatus of the sense of touch. Many instances are on 

 record of disease or injury to the central nervous system resulting in 

 complete loss of sensitiveness to pain, whilst sensitiveness to touch and 

 pressure remained undiminished. But there are no recorded cases, so 

 far as we are aware, of complete paralysis of the mechanisms of touch 

 and of the recognition of heat, of cold and of pressure, with the reten- 

 tion of normal sensitiveness to pain. Such a condition, if it were 

 established, would make it possible for an investigator to ascertain 

 whether skin-pain, by itself and unsupported by collateral evidence, has 

 a topographical meaning, or " local sign " ; and whether the expression 

 pain-spot may be legitimately used, as meaning a sounding spot in the 

 midst of a dumb area, and not merely a focus of sensitiveness at which 

 the weakest stimulus which can evoke pain is effective. 



Dr. Henry Head caused the large cutaneous nerve of the thumb- 

 side of the forearm and hand to be cut in his own arm, in order that 

 he might study carefully the revival of sensations which follows on 

 nerve repair. He found that, long before he regained the ability to 

 distinguish degrees of warmth, to feel as separate the two points of a 

 pair of compasses, or to recognize a touch with cotton-wool, he re- 

 gained his power of recognizing stimulation by agents that do harm — 

 hot things, cold things, pricking with a pin — but his power of local- 

 izing the spot injured was extremely vague. Trotter and Davies have 

 made similar experiments in their own persons on a still more exten- 

 sive scale and have confirmed and amplified Head's results. 



Investigations with the aid of new histological methods has shown 

 that the epithelial tissues are supplied with nerve-filaments in incon- 

 ceivable abundance. It is probable that the conclusion is justified that 

 every cell of the skin, of the mucous membranes, of the lining epi- 

 thelium of the air-chambers in the lungs, of the pleural and peritoneal 

 cavities, of the various glands, is connected with a nervous thread. It 

 is certainly true also of every muscle-fiber in the walls of the alimen- 

 tary tract, of ducts and of blood-vessels. By these filaments the cells 

 of the body-surfaces both external and internal, the central nervous 

 system and all motile organs, are bound together. 



Superimposed on this basal system are the various specialized sys- 



