 Meselson’s and Stahl’s caution was well justified, as we know now. For they did not know exactly what molecular species made up the bands they saw in their CsCl gradients. More recent considerations suggest that their DNA must have been fragmented, due to Meselson’s and Stahl’s use of a hypodermic needle to upload the DNA on their gradients. Such a treatment tears a whole genome from E. coli into little pieces. This fragmentation of the DNA would have ruled out the alternative interpretation with end-to-end linked molecules, had the scientists been aware of it at the time. In fact, without the shearing of the DNA before the density measurement the whole experiment wouldn’t have worked in the first place, due to the circular structure of the E. coli chromosome, which affects its density (Hanawalt 2004). What this shows is that there were relevant facts about the experimental system that Meselson and Stahl did not know, which makes it difficult to view this experiment as crucial.