where  the  evidence  of  the  crime  is  circumstantial,  or  not
clear  and  j^ositive  as  to  the  defendant's  identity  with  the  slayer.
In  the  case  of  Turner  v.  Commonwealth,^  on  a  trial  for
murder,  an  instruction  that  if  the  jury  did  not  think  an  alibi
had  been  proved,  "■  the  attempt  to  manufacture  evidence  was
a  circumstance  which  always  bore  against  the  person  making
it."  This  was  plainly  erroneous.  Where  the  case  rests  wholly
upon  circumstantial  evidence,  the  evidence  of  the  alibi^  though
not  clear,  should  be  submitted  to  the  jury  as  a  matter  of  de-
fence.
Sec.  513.  Proving  insanity.  —  The  question  as  to  the
sufficiency  of  the  proof  of  insanity  which  must  be  adduced,
and  as  to  the  effect  which  it  must  produce  on  tlie  jury  in
order  to  justify  a  verdict  of  acquittal,  is  not  universally
settled.  The  adjudications  upon  the  subject  may  properly  be
divided  into  three  classes,  as  follows ;  first,  it  has  sometimes
been  maintained  that  the  defendant  has  not  the  burden  of
proof,  and  that  the  presumption  of  sanity  only  arises  in  the
absence  of  all  evidence  to  the  contrary ;  but  that  his  only
duty  is  to  introduce  evidence  tending  to  cast  uncertainty
upon  the  question  and  thereby  to  raise  in  the  minds  of  the
jury  a  reasonable  doubt  as  to  his  sanity;  and  that  such
reasonable  doubt  is  a  sufficient  gi'ound  for  acquittal,  unless
ovei-come  by  affirmative  proof  of  his  sanity  adduced  by  the
prosecution.^      Second,    in    other   states    it   is    the   declared

1  86  Pa.  St.  54  (1878)  ;  s.c.  27  Am.  State,  37  Miss.  383  (1859)  ;  Hau-e  v.
Rep.  083.  State,  11  Neb.  537  (1881)  ;  s.c.  38  Am.
