Source : Webster's Revised Unabridged Dictionary (1913)

Lysis \Ly"sis\ (l[imac]"s[i^]s), n. [NL., fr. Gr. ly`sis.]
   (Med.)
   The resolution or favorable termination of a disease, coming
   on gradually and not marked by abrupt change.

   Note: It is usually contrasted with crisis, in which the
         improvement is sudden and marked; as, pneumonia ends by
         crisis, typhoid fever by lysis.

Source : WordNet®

lysis
     n 1: recuperation in which the symptoms of an acute disease
          gradually subside
     2: (biochemistry) dissolution or destruction of cells such as
        blood cells or bacteria
     [also: {lyses} (pl)]