_, second edition, p. 132).

The influence of lactation over the womb in preventing the return
of menstruation during its continuance is well known. According
to Remfry's investigation of 900 cases in England, in 57 per
cent. of cases there is no menstruation during lactation. (L.
Remfry, in paper read before Obstetrical Society of London,
summarized in the _British Medical Journal_, January 11, 1896, p.
86). Bendix, in Germany, found among 140 cases that in about 40
per cent. there was no menstruation during lactation (paper read
before Duesseldorf meeting of the Society of German Naturalists
and Physicians, 1899). When the child is not suckled menstruation
tends to reappear about six months after parturition.

It is possible that the divergent opinions of authorities
concerning the necessarily favorable influence of lactation in
promoting the return of the womb to its normal size may be due to
a confusion of two distinct influences: the reflex action of the
nipple on the womb and the effects of prolonged glandular
secretion of the breasts in debilitated persons. The act of
suckling undoubtedly tends to promote uterine contraction, and in
healthy women during lactation the womb may even (according to
Vineberg) be temporarily reduced to a smaller size than before
impregnation, thus producing what is known as "lactation
atrophy." In debilitated women, however, the strain of
milk-production may lead to general lack of muscular tone, and
involution of the womb thus be hindered rather than aided by
lactation.

On the objective side, then, the nipple is to be regarded as an erectile
organ, richly supplied with nerves and vessels, which, under the
stimulation of the infant's lips--or any similar compression, and even
under the influence of emotion or cold,--becomes firm and projects, mainly
as a result of muscular contraction; for, unlike the penis and the
clitoris, the nipple contains no true erectile tissue and little capacity
for vascular engorgement.[19] We must then suppose that an impetus tends
to be transmitted through the spinal cord to the sexual organs, setting up
a greater or less degree of nervous and muscular excitement with uterine
contraction. These being the objective manifestations, what manifestations
are to be noted on the subjective side?

It is a remarkable proof of the general indifference with which i