The Collaborative International Dictionary of English v.0.48:

Succus \Suc"cus\, n.; pl. Succi. (Med.)
   The expressed juice of a plant, for medicinal use.
   [1913 Webster]

   Succus entericus. [NL., literally, juice of the
      intestines.] (Physiol.) A fluid secreted in small by
      certain glands (probably the glands of Lieberk["u]hn) of
      the small intestines. Its exact action is somewhat
      doubtful.
      [1913 Webster]