This is a really cool and ingenious method for introducing functional macromolecules into adherent cell lines, and it has also been a good way to introduce foreign DNA into a cell line. You take a washed monolayer of the cells and incubate them in a buffered DNA solution. Then you scrape them with a rubber policeman (the scientific instrument, not an actual policeman made of rubber). Then, between 1 and 5 days later, you take the cells, and see if you were successful in achieving gene expression. Sometimes it ends up with up to 80% of the cells acieving DNA expression, and up to 70% cell viability can be obtained. Since it is inexpensive and fast, if you're just going to try to introduce foreign DNA willy-nilly, this is a good one to try first.