A comparative study was made of the character and severity of the infection produced by Tr. pallidum in groups of standard bred Havana, Dutch, English, Himalayan, and Rex rabbits. All known variables that might influence the course of the disease were common to the different breed groups.
On the basis of certain clinical data selected as criteria for the determination of variations in the response to syphilitic infection, it was found that the Havana and Dutch animals were resistant while the English, Himalayan, and Rex rabbits were susceptible.
From these results, it appears that breed, race, or family is a factor which significantly influences the response to infection with Tr. pallidum.