CHEMICAL CEPTORS 111 



tracts lowers the local resistance, infection is at once 

 inaugurated. Moreover, it is in the pelvis that the 

 defense mechanism of the peritoneum against infection 

 is most marked, being more efficient here than in 

 higher portions. This is the natural sequence of the 

 many hazards which have been encountered in the 

 pelvis, not alone from the accidents of childbirth, but 

 from the proximity of the fallopian tubes and the appen- 

 dix, infections of which always must have been com- 

 municated to the pelvic peritoneum. In this con- 

 nection the evolution of the omentum is of especial 

 interest. Just long enough to reach to the bottom of 

 the pelvis, apparently its only use is to move toward, 

 envelop and localize an infected point, thus serving as 

 a most valuable guardian to the whole abdominal 

 cavity. In its perfect altruism, the omentum may 

 fittingly be termed the philanthropist of the abdomen. 



In many other parts of the organism, and in many 

 pathologic conditions, we have convincing evidence of 

 the establishment, through natural selection, of cer- 

 tain specific chemical reactions adapted to the biologic 

 needs of the organism, which are equally remarkable 

 examples of its inherent ability to right itself auto- 

 matically when threatened by a menace from an inner 

 or outer environment. 



These specific chemical reactions, of which blood 

 coagulation and immunity against infection are among 

 the best known and most adequate, differ from ordinary 

 chemical reactions by reason of what seems to be a 

 kind of opportune team-work between isolated chemi- 

 cal substances evolved through natural selection. 

 These substances lie dormant in different parts of the 



