254 MAN --AN ADAPTIVE MECHANISM 



became infected. Had this state of affairs continued 

 long enough, then, by the law of natural selection, some 

 protective mechanism against infection would have 

 been evolved within the abdomen. The peritoneum 

 possesses such a mechanism, and we believe that the 

 phenomena of gas pain and of peritonitis are parts of 

 a self -defensive reaction. Since infection is most 

 readily spread and increased by movement, immobili- 

 zation of the abdominal muscles in the infected region 

 is a prime requirement in overcoming any abdominal 

 infection. Within the abdomen, immobilization is 

 secured (1) by the inhibition of the intestines ; (2) by 

 the distension of the intestines; (3) by the rigid and 

 persistent contraction of the abdominal muscles ; and 

 (4) by the exudation of a sticky, gluelike fluid. The 

 infected point is thus fixed by paralysis ; by disten- 

 sion ; by rigidity of the abdominal wall; and by gluing. 



On account of the intestinal inhibition, digestion 

 and absorption cease, and anorexia and vomiting fol- 

 low, as self-protective measures against the dangers of 

 poisonous, broken-down food products. Pain and ten- 

 derness play a part by forcing the maintenance of a 

 boxlike rigidity of the abdomen. 



As the abdominal walls are rigid, respiratory move- 

 ments are confined to the thorax ; and since the lungs 

 are thus but partially filled, the respiratory rate is in- 

 creased to compensate for the diminished volume of 

 exchanged gases. The increased H-ion concentration 

 due to increased energy transformation also tends to 

 increase the respiratory rate. The diminished respira- 

 tory excursion and consequent partial venous stasis in 

 the lungs predispose to pleurisy and pneumonia. 



