From a study of rabbits inoculated intratesticularly with two strains of treponemata derived from patients suffering from clinical yaws, it was found that a characteristic feature of the reaction to the infection was a well marked periorchitis of a granular or finely nodular type with or without a diffuse involvement of the tunic. While lesions of the testicular parenchyma also occurred they were relatively inconspicuous and consisted either of a minor diffuse orchitis which was usually followed by atrophy and fibrosis of the organ, or of small nodules; or there might be a combination of diffuse and nodular lesions. The granular periorchitis could be recognized clinically almost as soon as any change could be detected in the testicle, that is, about 3 weeks after inoculation; in the following month the covering of the testicle became studded with numerous tiny indurated nodules. Subsequently regression and healing took place and in the majority of animals no lesions were found 3 months after inoculation. In some animals residual lesions persisted for as long as 6 months. The granular periorchitis was a practically constant feature of the infection and was unlike any lesion of the tunic observed in experimental syphilis of the rabbit. Treponemata were numerous in the lesions of the tunic and somewhat less so in the testicle itself.

Dissemination of organisms to the uninoculated testicle and to the inguinal lymph nodes was demonstrated by animal inoculation although the clinical signs of a metastatic orchitis and periorchitis were slight and a lymph adenitis was an inconstant feature of the infection. Generalized lesions in remote parts of the body, similar to those occurring in experimental syphilis of the rabbit, were not observed.

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