Small pox vaccine was dropped on the scratched surface of the cornea of guinea pigs, and cellular studies were made on subconjunctival tissue. Observation after singular administration revealed only a slight proliferation in the histiocytes and fibrohistiocytes, while on supravital staining with neutral red, neutral red vacuoles were small in size. On the other hand when administration was repeated 14 days after the initial administration, proliferation of the histiocytes and fibrohistiocytes was remarkable, the neutral red vacuoles large in size and, although small in number, similar large vacuoles were seen in fibrocytes. Five days after the repeated administration, the neutral red vacuoles gradually declined in size, and among these vacuoles a small number of unstainable vacuoles were observed, which five days later were seen on the margin of the cell contour and gradually were seen to be excluded from the cell bodies. Repeated administration by dropping vaccine on the cornea, or by subcutaneous injection 30, 60, and 90 days after the initial administration revealed no remarkable changes in the cellular pictures of the subconjunctival or subcutaneous tissues, respectively.
