SOME PHYSIOLOGICAL RESULTS OF TEMPERATURE VARIATIONS. 129 
successful coition may always occur, or only at a certain period in connection 
with this rhythm, is uncertain. It appears, however, that about six days after 
menstruation most conceptions occur. 
The capacity of conceiving in a woman is then strongest (I.) between the 
ages of twenty and twenty-four; (II.) in the hottest season of the year; and 
(IIL.) about six days after menstruation. 
In conclusion, a few words may be said as to the mode in which temperature 
effects conceptions. 
Certainly not, as has been suggested, by raising the temperature of the body 
and of the uterine mucous membrane, giving thereby, as was supposed, more 
favourable surroundings to the sperms or ova. 
It is certain that a temperature about that of the body is most favourable to 
the life of ova and sperms ; but the difference of a few degrees would be very 
immaterial, the latter (the spermatozoa) living for many hours in active move- 
ment at the ordinary temperature of the air. 
Then again the difference in warmth of the interior of the human body varies 
little in the year. There is hardly a perceptable difference between the tem- 
perature in depth of winter or height of summer. 
It may be received as a fact, that there are external agencies, such as cold, 
heat, rain, wind, &c., which are, under certain conditions, antagonistic to life, 
and, when in action, they affect all of us. 
On the weak a force which will produce an overpowering result which we 
call death, will on the strongest have its effect, may be, only producing a slight 
depression of the natural energy. So that a district which has a high mortality 
is bad for the strongest, and a season which has a high mortality is also dan- 
gerous to all. 
Now, if the “death curve” be plotted in the same way as the “ conception 
curve,” it will be seen to be an inverted temperature curve in the main. As 
the temperature rises, the gross number of deaths diminishes. 
From our maxim, then, an increase of temperature is favourable to the 
health of all. The “health curve,” could we delineate such a thing, would, with 
the conception curve, correspond mainly with the temperature curve. Indeed, 
the increased capacity of conception is, we imagine, only an indication of an 
increased energy of the whole body, in which this function naturally shares. 
We must here remember that the power of producing offspring is a function 
which perhaps of all others is most taxing to strength, and therefore depends 
much upon physical tonus. 
A very rapid glance at the influence of temperature upon the power of 
reproduction in the lower animals, may not be out of place. With those of 
