Effect of hirudin on the tail bleeding time of wild-type and FcRγ^-deficient mice. Tail bleeding time was measured before and 5 minutes after hirudin (10 mg/kg) administration in FcRγ^–/– mice (2.5 ± 0.2 minutes before and 17.3 ± 2.6 minutes after, n = 10; P < .001, paired Student t test) or wild-type mice (2.0 ± 0.2 minutes before and 5.5 ± 0.7 minutes after, n = 10; P = .001, paired Student t test), as described in “Materials and methods.” Baseline tail bleeding times of a further 12 wild-type mice (total, n = 22) and 8 FcRγ^–/– mice (total, n = 18) were examined and demonstrated not to be significantly different from each other (P > .05). Horizontal bars represent the mean bleeding time values for each group of animals. *P < .05, Student t test.