88 MAN AN ADAPTIVE MECHANISM 



the brain from injury that if the skull has been pre- 

 viously opened under anesthesia, the brain of a con- 

 scious patient may be explored with a probe for a 

 tumor or other lesion without causing the slightest 

 pain indeed, the entire brain could be removed with- 

 out the patient's knowledge. 



After the extremities, the greatest shock-producing 

 areas of the body were shown to be the chest and the 

 abdomen. The deeper areas, the organs in the retro- 

 peritoneal region and the muscles of the spine showed 

 slight or no response to injury. Although injury to 

 the chest wall causes pain, the heart may be pierced 

 by a needle without pain. The heart, like the brain, 

 has had no phylogenetic opportunity to evolve pain 

 ceptors, and like the brain has always been a vital 

 organ, the penetration of which meant instant death 

 to the individual. The lungs likewise are pain-silent 

 to gun-shot wounds, stabs, contusions and punctures. 

 In opening lung abscesses no pain is caused by the 

 penetration of the lung tissue. 



Within the abdomen we found similar contrasts in 

 sensibility, and here, too, the type of trauma deter- 

 mined the degree of shock. Thus, in our experiments, 

 pulling upon, dragging and roughly manipulating the 

 stomach and the intestines caused an immediate fall 

 in blood-pressure, but a swift, keen incision, even the 

 crushing and burning of the inert organ, held gently 

 and carefully, caused no response. In the clinic a loop 

 of intestine has frequently been brought into a wound 

 for a few days and opened with a thermo-cautery, with- 

 out pain. Internal hemorrhoids may be painlessly de- 

 stroyed by burning. 



