This is a somewhat frequent disease, occurring not uncommonly in childhood and youth. The path by which the tubercle bacillus reaches the organ has not been unequivocally determined. The fact that the epididymis is usually the primary seat suggests an extension from the urethra, as in the case of gonorrhoeal epididymitis. But in the present case tuberculosis of the urethra does not precede that of the testicle, and it is difficult to believe that the bacilli can travel up the long urethra of the male and thence along the vas deferens, in both cases against the current of the fluid conveyed by these tubes, in order to lodge in the epididymis, and that without producing any disease in the passage. It is more probable that infection is through the blood, the condition being analogous to tuberculosis of the bones. This conclusion is confirmed by the fact that injury to the testis is undoubtedly, in some cases, an element in the causation.

As a general rule the tuberculosis begins in the epididymis. The result is great thickening and the formation of a caseous mass, enclosed very often in a firm fibrous capsule. Thus a firm elongated tumour may form behind and partly surround the testicle (see Fig. 473). In the testicle also caseous centres form, at first isolated, but afterwards running together into considerable masses. The caseous masses are very dense, but after a time they generally break down, and, having burst externally, tedious fistulae are the consequence.

When the testicle is examined in section the caseous structure is seen to be surrounded by a transparent grey tissue, in which tubercles are present. This inflammatory and tubercular structure by its pressure destroys the tubules for the most part, and portions of necrosed tubules are sometimes expelled along with the softened caseous material.

Tuberculosis of the testicle sometimes leads, after it has discharged externally, to a protrusion of the testicular tissue, constituting the so-called Fungus or Hernia of the testis. A similar result sometimes occurs in Syphilis. The dense tunica albuginea, when stretched by the new-formation, may force the tissue through the opening so that it protrudes externally. The protruded mass contains tubules, and is, in fact, the everted tissue of the testicle.

As previously mentioned, tuberculosis of the testis often extends along the vas deferens to the vesiculae seminales, prostate, and bladder, and sometimes from the bladder to the ureters and kidney. There is a tuberculosis along this whole course, and not a mere conveyance of the bacillus along intact channels.