86 WARFARE IN THE HUMAN BODY 



established by reaction which makes the trophoblastic 

 action physiological. 1 



That the influence of the ovum on the undeveloped tube 

 must have been of an exceedingly dangerous character is 

 now seen in tubal pregnancies during which the chorionic 

 villi frequently penetrate the wall of the tube, which does 

 not react as powerfully as the uterus. Such a process in 

 the uterus, which is itself a tubal dilatation, is now normal, 

 because these villi, the earlier nutrition roots or organs of 

 the parasite, are prevented from injuring the uterine wall 

 irrevocably by the transformation of the reactive uterine 

 decidua and the chorionic villi and the allantois of the 

 foetus into the combined temporary organ known as the 

 placenta. It may be noted that the non-placental mammals 

 are less exposed to the destructive and toxic effects of their 

 offspring, as they are born at an earlier stage than in the case 

 of the deciduate mammals. The marsupial foetus is about 

 half an inch in length when transferred to the milk-pouch. 

 It is impossible to look at the placenta without recognizing 

 that it is what we may call a compromise growth, one which 

 serves the embryo without destroying the parent hostess. 

 That all mammals are not yet fully armed against any 

 morbid alteration of function in the penetrating chorionic 

 villi is seen, as suggested above, in chorion-epithelioma, 

 where the energy of the villi trophoblasts leads to a 

 malignant overgrowth of the epithelial elements, which the 

 maternal tissues fail to inhibit. The hydatid mole, which 

 does not as a rule become malignant, is a case where 

 such inhibition has been sufficient. These phenomena 

 establish on a firm foundation the view that the uterus and 

 its reactions during gestation are definite protective pro- 

 cesses or variations springing originally from a purely 



1 See Chapter II., Malignancy, 



