Sorry Pam that was about pack horses. Here's a site with several of his medical books online.
http://books.google.com/books?id=uMQ0AQAAMAAJ&printsec=frontcover&dq=inauthor:%22George+Alexander+Otis%22&source=bl&ots=l3Ek6uUJLR&sig=IODLkJUo8uCFRIBhDhaVQEZC6t4&hl=en&sa=X&ei=2VZkUL-1IImW0QHLxYGIDw&ved=0CD0Q6AEwAg#v=onepage&q&f=false