Figure  5  illustrates  even  better  the  nature  of  the  cusp  movements
since  less  magnification  was  used.  In  this  case  the  heart  rate  was  also
slower,  and  a  period  of  diastasis  (G-A)  occurred.  The  valve  movements
alone  are  here  reproduced.  If  it  is  borne  in  mind  that  every  upstroke
of  the  curve  indicates  an  upward,  and  every  down  stroke  a  downward
movement  of  the  valve  cusps,  we  can  readily  obtain  a  vivid  mental
picture  of  the  exact  movements  undergone  by  the  mitral  cusps  in  the
normal  cycle.  It  is  clear  that  auricular  systole  and  ventricular  systole
each  produce  in  successive  order  an  upward  or  closure  movement  of
the  valves.  With  the  onset  of  auricular  systole,  probably  due  to  the
active  impingement  of  blood  upon  the  mitral  flaps,  a  slight  down-
ward movement  (AB)  usually  takes  place.  Then,  near  the  end  of
auricular  systole,  the  valves  move  upward  toward  the  position  of  clos-


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Fig.  4.  UppermoBt  curve,  ventricular  systole  (upstroke),  middle  curve,  auric-
ular systole  (upstroke) — lower  record,  movements  ot  mitral  cusps.  Speed  of
paper  2S  mm.  per  second.
Fig.  5.  Curve  showing  movements  ot  mitral  valves  when  normal  sequence
and  a  long  As-Vs  interval  obtains,  AC,  auricular  closure  of  valves,  DB,  ven-
tricular closure.
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214  ARCHIE    L.    DEAN,   JR.
ure  (C).  This  closure  is,  however,  only  temporary  and  not  complete,
the  valves  returning  promptly  to  their  former  open  position  (D),
At  the  onset  of  ventricular  systole,  the  valves  are  closed  completely
(E),  and  remain  so  during  systole  (EF).^  Having  returned  to  a  point
in  early  diastole  lower  than  they  occupied  previous  to  the  onset  of  ven-
tricular systole  (C),  the  cusps  gradually  rise  auricleward  during  the
period   of  diastasis   {GA).
