You need to buy glass slides with frosted, sandblasted ends (Fisher Scientific, Catalog N.  12-552). Frosting by painting (e.g.Superfrost) should not be used.
Pre-clean the slides by rubbing the edges of the slides against each other in medium, to get rid of the glass powder.
Slides can be autoclaved in advance for sterile dissociation.

Place a piece of spleen or a whole spleen cut in 2 or 3 pieces between the frosted ends of two glass slides.
Gently press and, with a circular motion, dissociate the tissue between the slides until is satisfactory.

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Thymus, lymph nodes, Peyer's Patches and fetal liver can be dissociated with this method.
Cells with intercellular junctions will disintegrate after dissociation with this method.

Filter with a fine mesh nylon filter.
Count viability.