Kaisa Turpeinen 



565 



lactating females of this strain of mice was, as numerous careful observations 

 showed, nineteen days. The prolongation of pregnancy was found by sub- 

 tracting this value from the observed length of pregnancy. 



In the experiments with hormones, they were injected subcutaneously, and 

 the injections were timed so that they took place before the calculated im- 

 plantation time, either normal or delayed. Injections were, however, not given 

 too soon after delivery in order not to influence the passage of eggs through 

 the Fallopian tubes, and they were not continued too long so that the lactation 



Number of young carried (.v,) 



Fig. 2. Dot diagram showing the relationship between prolongation 

 of pregnancy in days and number of young carried. 



process itself was not too greatly affected. The observed prolongation of 

 pregnancy was compared with the expected prolongation which lactation 

 alone would have caused and which was calculated from the equation: 



y = i: 20.\: -)- 0.30 (see below). 



Prolongation of Pregnancy During Lactation. In twenty-four cases of preg- 

 nancy during lactation, the length of gestation varied from twenty to thirty 

 days. As the normal length was nineteen days, pregnancy was thus prolonged 

 in every instance, the delays in parturition ranging from one to eleven days. 



These data make possible a study of the relationships between the prolonga- 

 tion of pregnancy and the number of young lactated or young carried. The 

 relationships are represented in the form of two dot diagrams (figs. 1 and 2). 



