To illustrate the importance of these points, we will describe the results of a recent experiment performed in our laboratory. A total of 1×105 fluorescent beads (FBs) (2.5 μm, λex: 630-660 nm, λem: 670-720 nm; Invitrogen) were suspended in 50 μL of phosphate-buffered saline and injected into the tail vein of Cby.CgFoxn1nu/J 1-month-old nude mice (Charles River). Location of FBs was registered by in vivo fluorescent imaging (Pearl-Impulse; LI-COR Biotechnology), at different times after the injection: 5 min, 1, 2, 3, and 4 weeks. After 4 weeks, the mice were killed according to approved methods, and their internal organs inspected for fluorescent emission. In order to localize with more precision the location of the beads, 10-μm tissue sections were analyzed by standard fluorescent microscopy (DMI 6000B; Leica Microsystems).