1754 HUMAN ANATOMY. 



lines pass onto its sides, leaving the termination of the gut without any peritoneal 

 covering. The branches of the inferior mesenteric artery in this region are the left 

 colica sinistra, which runs behind the permanent parietal peritoneum ; the sigmoid, 

 w^hich does the same until it reaches the part of the mesentery which is free ; and the 

 superior hemorrhoidals, which descend in the lower part of the original mesentery 

 until they reach the retroperitoneal area behind the rectum. 



PRACTICAL CONSIDERATIONS : THE PERITONEUM. 



The development, topography, and relations of the peritoneum have already 

 been sut^ciently described. It remains to consider its diseased conditions and those 

 in which it is an important or controlling factor in the production of disease in so far 

 as they are influenced by anatomical circumstances. 



Peritonitis is the most common and the most serious of peritoneal diseases. The 

 separate consideration of woimds of the peritoneum is not necessary, as traumatism, 

 unassociated with infection, produces merely hyperaemia and exudation. The pro- 

 cess is for convenience known as plastic or reparative peritonitis, a term also applied 

 to those forms of true (infective) peritonitis in which the bactericidal and absorptive 

 powers of the membrane itself and of its serum have resulted in the destruction or 

 the isolation of the invading bacteria. 



The anatomical routes by which bacteria may reach the peritoneum are : 



1. From without, as through an accidental or operative wound. 



2. From within, as from an escape of the micro-organisms through intestinal walls 

 leaky as a result of strangulation (as in intestinal hernias or volvulus or intussuscep- 

 tion) or of inflammation (as in appendicitis) ; or through an actual perforation, as 

 in gastric ulcer, typhoid fever, or intestinal cancer. 



3. Through the blood- or lymph-channels, as in many cases of tuberculous 

 peritonitis and possibly in so-called rheumatic, nephritic, and other clinical forms of 

 peritonitis, in some of which the infecting organism is still unknown. 



4. Through the Fallopian tubes. 



The peritoneum is not equally susceptible to traumatism or to infection on 

 both its surfaces or in all its parts. The external, areolar, or "wrong" side (page 

 1740 ) may be extensively separated from the subjacent structures (as in the extraperi- 

 toneal approach to the ureter or to the common iliac artery), or may be in contact 

 for a long time with an inflamed or a suppurating surface (as in perirenal or other 

 retroperitoneal abscess) without damage to the mesothelial or free surface of the 

 membrane, and with but little risk of the supervention of peritonitis. 



On the other hand, a small penetrating wound made with a dirty instrument will 

 probacy set up a diffuse and perhaps a fatal inflammation. 



The difference in results is due to the delicacy and vulnerability of the mesothe- 

 lial as compared with the fibrous surface ; to the great absorbent power of the former 

 {vide i?ifra), the area of which is about equal to that of the cutaneous surface of the 

 body, favoring toxaemia if the bacteria and their toxins are not destroyed or encap- 

 sulated ; to the excellent culture material supplied by blood-clot or by the injured or 

 necrotic epithelial surface ; and to the involvement in diffuse or spreading cases of the 

 peritoneal covering of the neighboring viscera, particularly the intestines. 



These facts determine the surgical rule that in doubtful cases of bullet and stab 

 wounds of the abdominal wall it is well — under aseptic conditions — to enlarge the 

 wound, ascertain the presence or absence of penetration, and cleanse or drain if 

 necessary. 



Not only are the two sides of the peritoneum thus unlike in susceptibility to in- 

 fection, but a similar difference exists between the parietal peritoneum and that cover- 

 ing the viscera. The former, applied by a layer of fat-containing connective tissue to 

 the relatively immobile muscular layer of the abdominal wall, is less easily inflamed, 

 or if inflamed develops a less diffused and less quickly spreading form of peritonitis 

 than does the thinner, more sensitive, and more vulnerable visceral peritoneum, 

 especially that covering the most mobile of the abdominal viscera, the small intestine. 



So, too, peritonitis originating in certain regions is, by reason of the facility 

 with which they may be shut off by adhesions, less threatening in its .course and 



