110 MAN --AN ADAPTIVE MECHANISM 



dium, in the liver, in the brain none of which has 

 evolved a chemical mechanism for defense. 



But what of the peritoneum itself, and of the organs 

 whose functions compel them to maintain communi- 

 cation with the outer environment? Certainly the 

 peritoneum has been constantly exposed to infection 

 from without through perforation, as well as to infec- 

 tion from the intestines, and should have evolved an 

 effective protective mechanism. Nothing could offer 

 more striking evidence of the fact that it has done so 

 than the phenomena which ensue when the peritoneum 

 is infected. These phenomena are a quick, local dis- 

 charge of free fluid laden with opsonins ; the formation 

 of an adhesive exudation ; the arrest of the peristaltic 

 movements, in order to prevent a further spread of the 

 infection; pain, incidental to the fixation of muscles 

 for the same purpose ; loss of appetite, to prevent the 

 intake of more food ; vomiting, to rid the stomach and 

 the upper portion of the intestines from decomposing 

 contents, which the inhibitory stasis has caused to 

 accumulate the entire complex response being ef- 

 fected through chemical ceptor stimulation. 



The successful defiance of infection by the genito- 

 urinary tract is well known. Here the uterus, vagina 

 and fallopian tubes keep constantly open a dangerous 

 passage-way to an environment laden with infection. 

 The gall bladder and bile ducts and the pancreatic 

 ducts connect directly with the intestinal field which 

 teems with infection. Yet through selection and 

 adaptation all these organs have become qualified to 

 maintain freedom from infection under normal condi- 

 tions. But if injury to the lining of any of these 



