In the 1st part, the author succeded in electron-microscopic ohservation of the capsule of Klebsiella pneumoniae. In the present part, by means of various experiments such as capsule swelling by immune sera, the author studied the characters of the bacterial capsule in detail. The results are briefly summarized as follows: 1) The cells of Klebsiella pneumoniae cultured on broth agar still has narrow capsule. By pouring immune sera, this capsule swells a little, and, at the same time, bacterial cell also somewhat swells making the horderhetween these two indistinct. 2) The capsule of Klebsiella pneumoniae passed through the mouse shows marked swelling after addition of imune sera. 3) To keep the capsular material as intact as possible. the following procedures were taken. Immune sera was directly dropped on hacterial colonies. a few minutes after this, bacterial cells float out, make the mesh with collodion membrane touch the floating cells. After lyophilizing thus obtained cells, the large capsule could be well observed electronmicroscopically. 4) A few minutes after addition of γ-globulin, the internal transparent layer of the capsular material of young culture can be observed more distictly: this is considered to be due to the retention of secretion by surrounding the cell with γ-grobulin. 5) The capsular swelling could he also observed in Diplococcus pneumoniae, but could not in Bacillus anthracis; this needs further atudies. 6) In some sorts of control non-encapsulated bacteria, these resuls could not he observed. From these observations, the author believes that the materials electron-micrcroscopically observed are nothing but the bacterial capsule itself.