176 
Proceedings of Royal Society of Edinburgh. [sess. 
typically healthy woman this organ, so long as it is free from the 
influences of gestation and lactation, is periodically for a greater or 
less length of time the seat of a regularly recurring functional 
variation in its molecular state, evidenced by the emission of a more 
or less marked haemorrhagic discharge, and which to all intents is 
its sole manifestation. The disturbance is evolved quite inde- 
pendently of the will, and apart altogether from any definable 
excitation. It appears to be induced spontaneously through the 
agency of an automatic nerve centre, and fails in consequence to 
produce any conscious sensation. When, however, the uterus be- 
comes the habitat of a developing ovum, or prior to this occurrence, 
and whilst segmentation is as yet progressing in the Fallopian tube, 
the waves of motion radiated by and from the germinal mass affect 
in a very decided manner the molecular state of the uterus, and 
determine a cessation of its routine function, and consequently of 
its regularly recurring manifestation of activity. Impregnation 
having resulted, other well-defined symptoms, in addition to that 
of the cessation of menstruation, are engendered, and help not only 
to guide the woman in arriving at a definite conclusion regarding 
her state, but aid us very materially in approximately estimating 
the duration of pregnancy. 
The symptoms associated with pregnancy to which I wish more 
especially to draw attention, as evidence of the existence of a genera- 
tive centre, and of its location in the medulla oblongata, are two — 
sickness and cough. It has been alleged, through the agency of 
experiments, that the sexual centre is located in the lumbar region 
of the cord. This opinion, however, appears to me to be founded 
on no very substantial basis. The mere fact that all, or nearly all, 
the sexual phenomena may be witnessed in animals after the lumbar 
portion of the cord has as far as possible been isolated by section is 
no very special criterion. The respiratory centre is located in the 
medulla, yet under special circumstances all the movements asso- 
ciated with respiration may be carried on after the medulla has been 
entirely removed. 
From the earliest period of existence every organism has been 
endowed with two distinct qualifications — 1st, that of maintaining 
self ; 2nd, that of perpetuating the species. At first, in the most 
primitive state, the double function was performed by a uniform 
