The # character

In reading about 'Netchannels' in Ocamlnet, I stumbled upon this code:
 

 let sum_up (ch : in_obj_channel) =
   let sum = ref 0 in 
   try 
     while true do 
       let line = ch # input_line() in 
       sum := !sum + int_of_string line 
     done; 
     assert false 
   with 
     End_of_file -> 
 
       !sum
 

 Which contains a # character. Using Google, it is very difficult to search for single characters. Thus I have currently failed to figure out what the # character does in Ocaml.
 

 What does it do?
 

 Is there a list on the web of all single characters that are significant in Ocaml? Another example could be the ! character.
 

 Keywords for future googlers: hash, sharp, hash tag, hashtag, sign, keyword,