Cauterize #4 nipple (Fig. B-F), blood vessel near junction by lymph node, and blood vessel at a point on the fat pad bridge between the #4 and #5 fat pads (Fig. B-D).

Use iris scissors to carefully excise and discard the triangular area defined by the cautery points (Fig. B). Developing mammary gland (Fig. B-E) has not grown past the lymph node (Fig. B-C) into the #4 mammary pads in 3 to 4 week old female mice. Removal of the above triangular area will result in a "cleared" #4 mammary fat pad into which tissues can be transplanted without interference from the host's mammary gland.