48 
AN EARLY HUMAN OVUM 
be so inconsistent with the character of the ovum itself and would involve 
so many gratuitous and unnecessary assumptions, that the case has the 
practical value of ascertained pregnancy after a single coitus. As the 
abortion began on November 4th and was completed on November 5th 
the total interval between coitus and expulsion is 16| days. 
While the time occupied by the spermatozoa in traversing the genital 
passages is not known in the human subject, the observation of Bireh- 
Hirschfeld 1 proves that they reach the Fallopian tubes in large numbers 
within 24 hours, and in the rabbit the distance from the vagina to 
the upper parts of the tube is known to be traversed in from a \ hour 
to 2 hours (Milnes-Marshall). It is therefore unnecessary to allow for an 
interval of more than 24 hours between coitus and fertilization. In those 
animals in which the phenomena have been actually observed, such as the 
mouse and the rabbit, fertilization occurs forthwith, and although the 
possibility of its being delayed is not denied in view of other facts of 
comparative embryology, there is no valid reason for supposing that it may 
not occur in the human subject immediately after the spermatozoa reach 
the upper third of the Fallopian tube, where it may be assumed that they 
normally encounter the ovum. 
There are no very reliable data regarding the length of time that 
spermatozoa may survive in the genital passages. They have been observed 
in a living state after nine days, but it by no means follows that they 
retain fertilizing power so long. The comparative infrequency of fertile 
insemination during continuous cohabitation, seems to point to there being 
some special circumstances connected with a successful impregnation. Were 
spermatozoa to retain for long their power of fertilization, no ovum 
should escape fertilization. It seems reasonable to assume, on the analogy 
of the lower mammals, that the favourable conditions are the occurrence 
of insemination and ovulation simultaneously or at no great distance of 
time. The shortness of the oestrus period in lower mammals may 
perhaps be looked upon as a means of attaining this end. If allowance 
must be made for the possible survival of spermatozoa for long periods, 
any attempt to establish a sequence of stages is futile. We proceed 
1 Cited from Leopold, Uterus und Kind, Leipzig, 1897. 
