128 JOHN BERRY HAYCRAFT ON 
It may be asked, What right have we to say that the influence of pee 
ture is on conceptions and not on insemination ? 
The answer is not difficult, for the interval between coition and delnean 1s 
greater (275 days) than our interval (272 days) between conception and delivery. 
The coition would therefore fall behind the temperature curve, therefore not 
affected by it. No doubt there may be some influence on the number of 
coitions, but this influence is not great enough to be shown. 
Law of Capacity of Conceiving. 
The facts that we have gleaned about the influence of temperature upon 
conception, enable us fully to state as a law the capacity of conceiving of women 
during different periods of their life. | 
There are three factors which are to be considered as modifying this capacity, 
namely, 
(I.) Time of Life. 
(II.) Temperature. 
(III.) Menstrual Rhythm. 
(I.) Time of Life. (For particulars consult “Fertility, Fecundity, and 
Sterility,” by Dr Marruews Duncan.) 
This influence effects woman’s capacity in that the sexual organs are only 
gradually developed as age advances; at a certain period they are developed 
fully, and then undergo a gradual involution. 
At birth the capacity is nothing ; it remains so until puberty, when capacity 
first appears. 
This increases with age until between twenty and twenty-four, when the 
maximum is reached. The capacity then weakens until about the fortieth or 
forty-fifth year, when it becomes, as at birth, nothing. 
This will be seen better on referring to the following curve (Chart IV.). 
This curve is however modified by the other factors; and the result, given 
when all the factors are considered, gives a curve such as is represented in the 
figure, where one year of the previous curve is depicted with the other ones 
superimposed (Chart V.). 
(II.) The Effect of the Temperature Curve is to give a maximum every summer, 
giving the age curve (Chart V.) a wavy appearance, with a crest and trough 
every year. 
How this temperature influence is exerted will be considered hereafter. 
(III.) The Menstrual Rhythm occurs twelve times in the year, and gives 
twelve maxima to Chart (V). About its influence little is known, whether a 
