64 PHYSIOLOGY CHAP. 



sensitive along the urethral canal, particularly in the pro-static or 

 membranous part ; that of the bladder, 011 the contrary, has little 

 sensibility. Even large calculi may remain unperceived for some 

 time until inflammation sets in. The vulva is sensitive, but the 

 vagina, cervix of the uterus, and the uterus itself are only 

 moderately sensitive. As long as they are normal they can be 

 cut or cauterised without producing pain. Pain in these parts 

 undoubtedly depends on compression or traction of the sensory 

 nerves that lie in the depths of the tissue, or in the uterine 

 appendages and the vaginal canal. 



The excretory ducts of the glands are usually very sensitive 

 to distension. The intense pain of hepatic and nephritic colic is 

 well known. 



The heart, arteries, and veins are insensitive to pain in the 

 normal state. The same may be said of the hepatic parenchyma, 

 spleen, pancreas, kidneys, and lymphatic glands. The genital 

 glands, the testicles, the ovaries and their appendages are, on the 

 contrary, highly sensitive. Compression of these parts causes 

 acute pain, and may even induce syncope. 



From all these facts it is clear that the internal tissues and 

 organs have as a rule a lower sensibility to pain than the surface 

 of the body ; and that the deep organs innervated by the 

 sympathetic normally feel little pain, but they have a very high 

 latent pain sensibility which may become apparent under abnormal 

 conditions, particularly in inflammation. 



Lennander (1902-4), on the basis of a new series of clinical 

 observations, opposed this hypothesis, and maintained that the 

 difference of sensibility shown by the internal tissues, according 

 as they are in normal or pathological states, is to a large extent 

 apparent only. According to his observations, the pains that 

 can be produced in the abdominal cavity must be referred to the 

 parts innervated by the lumbar and sacral nerves, particularly 

 those to the parietal peritoneum. This is sensitive under both 

 normal and abnormal conditions, especially to mechanical stimuli 

 (traction, dilatation) ; while the whole of the intraperitoneal viscera 

 and the visceral peritoneum which covers them are, on the 

 contrary, incapable of initiating pain either in the normal or the 

 pathological state. When these viscera are diseased, the pains 

 do not indicate exaggeration of their normal obscure sensibility ; 

 they remain insensitive, but transmit the irritation to the sensitive 

 parietal peritoneum, either by an exaggerated peristalsis, or by 

 meteorism or abnormal distension of the intestinal canal, by the 

 traction due to inflammatory adhesions, or lastly by the produc- 

 tion of toxines or irritative chemical products. The hyperalgesia 

 of the parietal peritoneum caused by these products fully explains 

 the fact that in acute abdominal diseases the weakest stimuli may 

 provoke very intense pain. 



