ii SENSIBILITY OF THE INTERNAL OEGANS 63 



compact substance, is insensitive, as proved in amputations without 

 chloroform. The pain sensibility of bone-marrow under physio- 

 logical conditions is doubtful. 



The muscles in the normal state are but little sensitive to 

 pain. During amputations without anaesthetics they give no 

 pain. Strong compression gives rise to a specific dull pain ; 

 intense faradisation is very painful. This sensitiveness to pain is 

 not due to excitation of the cutaneous nerves, because Duchenne 

 observed it with direct electrical stimulation of the pectoralis 

 major muscle exposed during excision of the breast. The feeling 

 of muscular fatigue presents every gradation from a simple sense 

 of heaviness to acute pain, which may last 24-48 hours, and is 

 accentuated on the slightest pressure. But in this case the state 

 of the muscle is evidently altered, owing probably to the 

 accumulation of fatigue products, which act as an irritant poison. 

 Similar abnormal conditions underlie the muscular and articular 

 pains of a rheumatic and gouty character. On the other hand, 

 the sharp pain that accompanies the cramp caused by violent and 

 involuntary contracture of the muscles is transitory. It has been 

 attributed to the compression of the cutaneous sensory nerves 

 that traverse the muscles, but this is a fallacy, because in that 

 case, in accordance with the law of peripheral projection, the 

 pain would be perceived in the skin and not in the contractured 

 muscle. 



Serous membranes in general, as the peritoneum, pleura, 

 cerebral and spinal dura mater, and the synovium, are believed to 

 be sensitive to pain even under normal conditions, and when 

 inflamed become much more so. 



The pain sensibility of the mucous membrane of the digestive 

 tract is generally very acute near its junction with the skin (oral 

 and pharyngeal cavities), but it diminishes in the oesophagus. 

 The painful sensation of choking produced when an alimentary 

 bolus that is too large or too hard sticks near the cardiac aperture 

 of the stomach is not due solely to the sensibility of the mucous 

 membrane, but rather to the cramp that compresses the nerve 

 fibres that surround the canal. The pain sensibility of the 

 stomach is moderately acute, that of the intestine low, but it 

 increases again in the rectum and at the anal orifice. Puncture, 

 section, cauterisation (as shown by experiments on rabbits and 

 dogs, and surgical operations in man), do not produce true 

 sensations of pain in any part of the intestinal canal under normal 

 conditions. But in a pathological state, the intestine may become 

 the seat of severe pains, such as those of colic. 



The mucous membrane of the respiratory apparatus is sensitive 

 to pain in the nasal and laryngeal tracts, but insensitive through- 

 out the bronchial ramifications. 



The mucous membrane of the ureto-genital system is very 



