420 FEANKLIN P. MALL 



8th to 16th day of the menstrual cycle it was entered for each 

 of these days. 



It is noteworthy that there was no entry for the last seven 

 days of the menstrual month, indicating that pregnancy did not 

 take place either a week before this nor within the week following ; 

 that is, there is a sterile period of about 18 days and a fertile 

 period from the end of menstruation to the 15th day, which 

 includes the probable time of ovulation. Of course only those 

 cases which came to the maternity hospital could be recorded, 

 and it is interesting to note that none of the 100 pregnancies dated 

 from a furlough during the last week of the menstrual month. 

 Such did not end in conception. Siegel was able to gather 10 

 cases in which the husband was on furlough a few days before 

 the menstrual period, and in none did pregnancy follow. He 

 cites further cases gathered by Wohler from the records of the 

 same maternity hospital for the past ten years. These included 

 160 pregnancies among newly married women, in whom con- 

 ception had occurred during the first five weeks after marriage. 

 Among this group there were 65 cases in which marriage took 

 place within the eight days preceding the menstrual period, and 

 in each of them one more menstruation followed, which fact 

 alone would indicate a sterile condition during the week pre- 

 ceding it. The records of Siegel, although not entirely satis- 

 factory, demonstrate quite conclusively that the most probable 

 time for conception is during the week or ten days after the 

 period of menstruation. 



From what has been written above we may, for the sake of 

 argument, accept one day as the average time between copulation 

 and fertilization. The time at which this is most likely to occur 

 is between the 4th and 13th day after the first day of menstrua- 

 tion, as shown by the following table. This table is compiled 

 from the records of our own cases, given above, each datum being 

 obtained by subtracting the copulation age from the menstruation 

 age. A similar result is obtained by dividing the total number of 

 days by the number of cases, which equals exactly 13. That is, the 

 average copulation date is the 13tli day after the beginning of the 

 last menstrual period. The figures upon which this result are 



