1) Fluorochrominized tissue culture of spleen was established by the similar method used for bone marrow culture devised in our clinic. And vital observation of splenic reticulum cells was done by fluorochrominized tissue culture method by the use of rectangular cover slip method which has been mentioned in the chapter I. 2) Each type of reticulum cells showed characteristic fluorochrominized findings when stained with acridine orange. Granules and vaculoles stained with acridine orange showed nearly similar findings to neutral red granules and vacuoles as described in the chapter Ⅱ. 3) By this method, the existence of transitional forms between each type of reticulum cells and maturation process were confirmed in the series of types Ⅰ, Ⅱ and Ⅲ reticulum cells, as have been already described by other methods in the chapter Ⅰ and Ⅱ. 4) Part of acridine orange stainable vacuoles were thought to be secondary to toxic effects of acridine orange stain. 5) Changes of fluorochrominized granules and vacuoles were observed successively in the degenaration of type Ⅲ reticulum cells.