THE USE OF CENTRIFUGATION IN BIOLOGY 89 



Exp. no. 



2 

 1 

 1 

 1 

 2 

 2 

 2 



U .. . 



M* and 1.9 



— J ^ — ^ mixed 



(b) 



and 4.1 

 mixed 



Fig. 43. The actual figure on which Fig. 42 is based. (From Meselson and 

 Stahl, Proc. Natl. Acad. Sci., U.S., 44, 671, 1948; courtesy the authors and 

 National Academy of Sciences.) 



rials always persist. After the parental molecules have separated into 

 two pieces, they do not separate further; there are no molecules of any 

 density intermediate between these "half-dense" molecules and normally 

 light molecules. Accordingly, w T e conclude that a semiconservative mech- 

 anism of replication is operating, and the Watson-Crick model has yet 

 another piece of supporting data. For your study, the actual data pub- 

 lished by the researchers is presented in Fig. 43. 



