We study the dynamics of information propagation in environments of
 low-overhead personal publishing, using a large collection of weblogs
 over time as our example domain. We characterize and model this
 collection at two levels. First, we present a macroscopic
 characterization of topic propagation through our corpus, formalizing
 the notion of long-running "chatter" topics consisting recursively of
 "spike" topics generated by outside world events, or more rarely, by
 resonances within the community. Second, we present a microscopic
 characterization of propagation from individual to individual,
 drawing on the theory of infectious diseases to model the flow. We
 propose, validate, and employ an algorithm to induce the underlying
 propagation network from a sequence of posts, and report on the
 results.