182 THE ACTION OF THE LIVING CELL 



gestation. This fact signifies one of two things : either 

 the mother develops an immunity towards cytost, or 

 the production of cytost by the fetus ceases. In order 

 to analyze these concepts, let us return to Hartman's 

 observations on the monkey, where it was found that 

 the egg digs into the maternal tissues until half buried. 

 Since, as we have seen, this implantation is accom- 

 panied by autolysis, we may inquire why this autoly- 

 sis does not continue until all the uterine tissues have 

 disappeared. Two answers to this perplexing ques- 

 tion suggest themselves. Either the stimulus of autoly- 

 sis, the fetus, has undergone a change, or the mother's 

 tissues have become resistant towards the invasive ac- 

 tion of their offspring. Each of these answers con- 

 tains an element of truth, as is evidenced by the fol- 

 lowing considerations. 



In the previous discussion we have shown that the 

 repeated injection of small quantities of cytost leads 

 to the development of an active resistance towards 

 this substance, presumably through the development 

 of an anticytost. With this in mind we may postulate 

 that because of the slow and continual absorption of 

 cytost from the disintegrating uterine tissues, the 

 mother's resistance to this substance is raised in a 

 manner analogous to that resulting from the regular 

 injection of small quantities of homologous cytost. 

 That such a resistance is developed during preg- 

 nancy is shown by the following considerations. 



Injection of cytost in suitable quantity into preg- 

 nant cats causes nausea and retching which usually 

 pass off within an hour. When like quantities of cy- 

 tost are injected into male cats kept under the same 

 conditions in the laboratory, vomiting and retching 



