As the list has been a bit quiet I thought I'd briefly mention an 
article I found in The New Yorker, "When a Virus Is the Cure". It's 
about a therapy for treating bacterial infections.  I found it 
particularly interesting as I'm currently reading Susan K. Harris' "Mark 
Twain, the World and Me".  She mentions Twain's puzzlement over cholera 
- or lack of cholera in the Ganges downstream of Benares.  She goes on 
to discuss this very therapy and how it may begin to find acceptance in 
today's science and Twain's "willingness to doubt Western scientific 
thinking on the basis of Hankin's empirical evidence.  It is one of the 
places in "Following the Equator" where we see a crack in Twain's faith 
in the Empire's self-justifications."

Harris' book is fascinating for a whole lot of additional thoughts.  I'm 
going to need to add a lot of comments throughout my Twain's Geography site.