luid may be evacuated by tapping the scrotum. When a
hydrocele is found to be congenital, it must be at once obvious that to
inject irritating fluids into the tunica vaginalis (the radical cure) is
inadmissible. In an adult, free from all structural disease, and in whom
a congenital hydrocele is occasioned by the gravitation of the ordinary
serous secretion of the peritonaeum, a cure may be effected by causing
the obliteration of the serous spermatic canal by the pressure of a
truss. When a congenital hydrocele happens in an infant in whom the
testicle, 5, Fig. 1, Plate 39, is arrested in the inguinal canal,
[Footnote 2] if pressure be made on this passage with a view of causing
its closure, the testicle will be prevented from descending.

[Footnote 1: The serous spermatic tube remains open in all quadrupeds;
but their natural prone position renders them secure against hydrocele
or hernial protrusion. It is interesting to notice how in man, and the
most anthropo-morphous animals, where the erect position would subject
these to the frequent accident of hydrocele or hernia, nature causes the
serous spermatic tube to close.]

[Footnote 2: In many quadrupeds (the Rodentia and Monotremes) the testes
remain within the abdomen. In the Elephant, the testes always occupy
their original position beneath the kidneys, in the loins. Human adults
are occasionally found to be "testi-conde;" the testes being situated
below the kidneys, or at some part between this position and the
internal inguinal ring. Sometimes only one of the testes descends to the
scrotum.]

[Illustration: Abdomen and scrotum, showing bone, blood vessels
and other internal organs.]
Plate 40--Figure 1.

PLATE 40, Fig. 2.--The serous spermatic canal closes imperfectly, so as
to become sacculated, and thus a hydrocele of the cord is formed.--After
the testicle, 7, has descended to the scrotum, the sides of the serous
tube, or lining of the inguinal canal and cord, 6 b, 6 c, may become
adherent at intervals; and the intervening sacs of serous membrane
continuing to secrete their proper fluid, will occasion a hydrocele of
the cord. This form of hydrocele will differ according to the varieties
in the manner of closure; and these may take place in the following
modes:--1st, if the serous tube close only at the internal ring, 6 a,
while the lower part of it, 6 b, 6 c, remains pervious, and
communicating with the tunica vaginalis, 6 d, a hydrocele will be formed
o