SOME PHYSIOLOGICAL RESULTS OF TEMPERATURE VARIATIONS, 127 
It is only by most careful working with different sets of data, and with more 
exact ones than those of Scotland, that a final decision can be arrived at upon 
so nice a point, where the difference of a day or two is everything. 
When sufficient data are at hand, this matter will receive further attention. 
Scientifically defined, the “duration of pregnancy” is the length of time 
which elapses between conception (not insemination) and delivery. 
Now one knew nothing before about the time when conception occurs, and 
therefore nothing exact about the “ duration of pregnancy.” 
Statistics tell us that the time between “insemination ” and delivery is, on 
an average, 275 days. Now, however, by the temperature curve, we have an 
indication of when conception occurs. 
All we have to do is to find out exactly how far we must put back the birth 
curve in order to get the primary and secondary curves—FourRIER—ewactly to 
correspond to the similar curves; to do, in fact, exactly what we have already 
done roughly when we put the birth curve back nine months. 
This interval is the “ duration of pregnancy.” 
When analysed it will be remembered that the primary curve maximum was 
at 183° and the secondary at 53°; while the corresponding temperature curves 
give 185° and 55°. 
The difference in both cases is therefore 2°. They show therefore conclu- 
sively that the birth curve has been put back 2°, or =25th of a year, or a little 
more than two days too much. 
To make them agree exactly, it should have been put back 175° or 272 days, 
This 272 days elapses between conception as indicated by temperature curve, 
and delivery as given in the Register-General Reports. This 272 days is the 
duration of pregnancy. Now, it is already known that the average interval 
between insemination and delivery is 275 days; therefore 275 — 272 = 3 days 
is the time which elapses between insemination and conception. 
| These facts, important in their physiological bearings, enable us to construct 
' a complete table, showing the intervals between all the physiological processes 
concerned in the birth of a child. 
We have the time between 
Last menstruation and delivery = 278 days (Marr. Duncan) ; 
Insemination and delivery = 275 days (Matt, Duncan) ; 
Conception and delivery = 272 days. 
Insemination (which is to be followed by conception) then occurs three days 
on the average after last menstruations ; conception follows this in three more 
days; and delivery in 272 days. 
VOL, XXIX. PART I. 2K 
