Kaisa Turpeinen 569 



lactating and pregnant mice prolong the span of gestation still more than 

 lactation alone, and given in large doses may entirely prevent pregnancy, 

 presumably because of too excessive delay of implantation. 



Discussion 



There seems to be a reciprocal effect in the relationship between lactation 

 and the implantation process. From the work of Frankl"^ we know that trans- 

 plantation of placentas into pregnant animals near term inhibits lactation. 

 On the other hand, lactation has an inhibiting effect on implantation by 

 delaying it. The action of lactogenic hormone and corpus luteum hormone 

 prevails during lactation. These facts and the results of my work support the 

 view that the excessive production of lactogenic hormone and corpus luteum 

 hormone during lactation wotdd be the cause of delayed implantation. 



Summary 



The prolongation of pregnancy, which occurs in some species of lactating ro- 

 dents and which is due to the delay of implantation, has been studied. Particu- 

 lar attention has been given to the effect on the prolongation of pregnancy 

 of progesterone and hypophysial lactogenic hormone administered during the 

 first part of the pregnancy, that is during the implantation time. Albino mice 

 were used as experimental animals. The hormones were injected subcuta- 

 neously, and their effect on the prolongation was noted. Before starting the 

 experiments with hormones, the effect of the number of young on prolongation 

 of pregnancy during lactation was studied. 

 The following conclusions were reached: 



1. In accordance with the majority of earlier workers, it was found that the 

 length of pregnancy in lactating mice is dependent on the number of young 

 the mother is suckling. There is an almost perfect positive correlation between 

 these two variables (r= -1-0.928). Each of the young lactated prolongs the 

 pregnancy on the average by 1.2 days. 



2. There is no demonstrable correlation between the delay and the number 

 of young carried. 



3. The synthetic corpus luteum hormone (progesterone) causes a further 

 prolongation of pregnancy, that is, the length of pregnancy is prolonged be- 

 yond what lactation alone would cause. 



4. The injection of the hypophysial lactogenic hormone causes further pro- 

 longation of gestation during lactation. Given in larger doses it may entirely 

 prevent littering. 



I wish to express my gratitude to Dr. Carl G. Hartman for suggesting this 

 problem and for his aid during the early part of the work. 



Since Dr. Turpeinen's return to her fatherland, it has been found by two experimenters. 

 Dr. Segar-Jones at the Johns Hopkins Medical School, working with the mouse and rat, and 



