摘要： Four groups of mice (Group Ⅰ, 8 mice immunized 3 times before challenge; GroupⅡ, 11 mice, immunized twice; Group Ⅲ, 12 mice, immunized once; Group Ⅳ, 12mice, not immunized) were challenged and then examined with indirect fluorescentantibody test to observe the relationship between the functional immunity level and