This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteriology, Subject name: Microbiology
T.pallidum can be grown in 
Select and explain. 
A. Mice, B. Armadillo, C. Rodent, D. Rabbit
D: Rabbit
Answer: D: Rabbit 
Explanation: Virulent Treponema pallidum strains cannot be cultivated in aificial media but have been maintained for many decades by a serial testicular passage in rabbits. One such strain (Nichol's strain), isolated from the brain of a fatal case of general paralysis of the insane in 1912, is still being propagated and used for diagnostic and research purposes.(Ref: Ananthanarayan 9th edition, p372)