One and two-step transition probabilities.

The 27 target sites listed in decreasing order of their edge weights (ensemble average values) from lung site. The 20 sites above the ‘cut-off’ are called ‘First-Order’ sites. Their direct connections from the lung are strong enough so that they represent the most likely route to that site. The 7 sites listed below are called ‘Second-Order’ sites. Their connections from the lung are sufficiently weak that it is equally or more likely (taking into account standard deviations) to get to the site via some other first-order site (shown in parentheses).