THE RECEPTORS 8G5 



The brain substance and pia arachnoid are insensitive on the convexity 

 of the brain and beneath the occipital bone, but pain may arise from it 

 beneath the frontal bone and toward the zygomatic arch. In the thoracic 

 cavity the visceral pleura, which is innervated by the vagus and sym- 

 pathetic, is insensitive to the pressure of a stiff wire. The parietal 

 pleura, innervated by the intercostal nerves, is the seat of pain which is 

 accurately localized. The peripheral portion of the diaphragmatic pleura 

 is innervated by the intercostal nerves over a band about two inches 

 wide. Pain arising in this region is referred to the lower thorax, the 

 abdomen and lumbar region. The central portion of the diaphragmatic 

 pleura, innervated by the phrenic nerve, is the seat of pain referred to 

 the neck. The lungs are insensitive, as is the heart, except under trac- 

 tion. In the abdomen all organs receiving a nerve supply only from the 

 sympathetic nerves and from the vagus below the branching of the re- 

 current nerve have no sensation. The substance of the stomach, intes- 

 tines, and liver may be cut into without causing discomfort. The fibrous 

 capsule and parenchyma of the kidney do not give rise to sensation if 

 the fatty capsule is removed. The bladder may be cut or pinched, but 

 not pulled, without giving pain. 



It must be remembered that these observations have been made on 

 individuals undergoing operation with local anesthetic. Sensitivity may 

 have been modified by exposure of the organs to the air, or by spread of 

 the anesthetic. They give valuable information from a surgical point 

 of view, but do not tell us about the conditions which give rise to sen- 

 sation during the normal or pathological activity of the viscera. It 

 will be noted that the most adequate stimulus for visceral pain is trac- 

 tion, which may produce discomfort when cutting is ineffective. It is 

 probable that the pains of labor, menstruation, colic, gastric ulcer, etc., 

 are set up by tension within the muscles of the uterus, or gastrointes- 

 tinal tract, or to traction upon the mesenteries and their insertion into 

 the parietal peritoneum by the arching of these organs when their walls 

 attempt to contract while in a distended condition. 



The sensibility of the mucosa of the stomach has been made the ob- 

 ject of extensive study, particularly in men possessing gastric fistulas. 

 The mucosa is quite insensitive to pain, when pricked with a pin or 

 pinched. Pain is felt as the result of such stimuli only when they are 

 sufficiently severe to spread to underlying structures. The mucosa is 

 also insensitive to touch. A stiff test tube brush may be thrust into 

 the stomach and moved about vigorously without producing any sen- 

 sation. On the other hand, the temperature senses are represented in 

 the wall of the stomach. The introduction of water below 10 C. pro- 

 duces a sensation of cold, and above 50 one of heat. Intermediate tem- 

 peratures are without effect. 



