FERTILITY 219 



I have tried to bring together the modern evidence 

 that bears on the problems of fertility and sterility. 

 It is evident that there are many obscure relations that 

 need to be explained. I fear that, owing to the diffi- 

 culty of summarizing this scattered and diverse ma- 

 terial, I have failed to make evident how much labor 

 and thought and patience has been expended in ob- 

 taining these results, meager though they may appear. 



But while it is going to take a long time and many 

 heads and hands to work out fully these problems, there 

 can be little doubt that the modern method is the only 

 one by which we can hope to reach a safe conclusion. 



