In addition to macroscopic inspection and conventional staining,histochemicaltechnology and scanning electron microscopy were used to observe sequential morpholog-ic changes in the IBD immune process and further our knowledge of IBD.The resultsshowed that IBD vaccines of medium virulence should preferably be selected for use in areaswhere IBD was prevalent.Whether the damaged bursa would be repaired depended on thefollowing two factors:portion of lymphoid tissue remaining after damage to the bursal lym-phfolliculi,and whether or not the regeneration of the bursa occurred before bursa involu-tion.