A polymerase chain reaction (PCR) having high specificity and sensitivity was estibilished for detecting toxoplasma gondii (TOX) in laboratory animals, according to designing primers. The results showed that TOX might exist in rabbits (3/60) useful for teaching, which came from countryside. These findings suggest that the infection of TOX might be paid more attention in the aspect of laboratory animals. Key words TOX PCR mathematical statistics that the probability distribution of measured data obeys normal distribution. By the great difference in elastic moduli between cementum and dentin it is explained that 1 why more cementum grows at the root apexes;2 the behavior of cementum must be taken into consideration when the stress analysis for teeth is carried out.