By this name is meant the accumulation of fluid in the tunica vaginalis. The fluid is serous and the cause of its accumulation is believed by some to be inflammation. On the other hand the absence of pain and the infrequency of adhesion of the sac are in favour of a non-inflammatory origin, and the hydrocele may be the result of a local dropsy to which the dependent position of the sac predisposes. Cases of Acute hydrocele have been observed in which the disease is undoubtedly inflammatory, flbrine being deposited on the surface as well as fluid accumulated in the sac.

In ordinary Chronic hydrocele fluid slowly accumulates and distends the sac, and so a bulky tumour is formed which is pear-shaped with its blunt end downwards. The fluid is usually a clear serum with a specific gravity of 1022 to 1024, but sometimes it is slightly opalescent. In the true hydrocele this is not from the presence of spermatozoa, but from the existence of fine fat drops, resulting from degeneration of the leucocytes floating in the fluid. There may even be cholestearine crystals formed in this way.

Not infrequently haemorrhage occurs, most commonly as the result of a blow or other injury, and the hydrocele becomes a Hematocele. The blood mostly coagulates, and the coagulum through time undergoes various changes, softening into a brown pultaceous material or into a brown turbid fluid, in which are enormous numbers of cholestearine crystals. The blood seems to act as an irritant to the tunica vaginalis, causing often a very great thickening of it. The interior also is rough and sometimes presents considerable projections. The thickened cyst may contract somewhat so that the tumour is reduced in size. This thickening of the wall, even when the contents are fluid, may cause the hematocele to be mistaken for a solid tumour, and castration has often been performed under this belief.

A hydrocele or hematocele may be cured by the fluid being absorbed, the result being adhesion of the opposed surfaces of the tunica vaginalis and obliteration of the sac.

In the condition named Congenital hydrocele the tunica vaginalis retains its communication with the peritoneal cavity. The fluid may come from the peritoneal cavity, or may originate as in an ordinary hydrocele. It can be pressed into the peritoneum through the neck. It will be understood that a congenital hernia may coincide or alternate with this form of hydrocele.