60
IVAN GOODBODY
claimed thcit, t,here is a reliiy centrr in the middle dividing the heart
functionally into two pclrte. 1 hnvc ~ l s o observed an apparent relay in
the heart of Corelln rcrillmerinna hiit it is most likely, as suggested by
Hecht (1918c), that it is drir to a shifting of the position of the raphe
and this givcs a fiilse imprcwion of the existence of such n centre.
Reversal of the hetrrt may takc plticc. immediately without, any pausc,
there may be a pnuw of varying duration between opposing waves,
or the two opposing waves may momentarily collide at the centre of the
heiirt beforcl the new wave comes to dominate the other.
The peristaltic wave of cotitrartkm forces blood out of the heart but
in a valveless system it is not easy to see how diastolic filling of the
heart is achieved nnd what prevents backflow through the system. In
the absence of elastic fibres or other attachments there must be other
mechanisms for refilling the Iieert. If the pericardium is punctured the
heart immediately swells iitdicating that it must normally be held
under pressure by the pericardial fluid. Skramlik (1929) was the fist to
point out that presRure in the periclardial fluid was necessary for proper
functioning of the heart and this wns later confirmed by Benazzi (1935).
Skramlik determined that the optimum pressure in the pericardium
was 2 cm water but Kriebel (1968a) found that the optimum is 5 cm
water. Kriebrl also pointed out that this pressure is responsible for the
production of >I contraction valve by forciag the wall of the heart into
the venous ostiuni. As pressure rises in the circulatory system the
venous ” prcssure comes to e x c ~ ~ e d
the pericardial pressure and forces
open the “ virlve ” and refills the heart.
L C
C . Pworrt aker act ivily
l‘hc rhyt hmir alteration of hetirt beat suggests the existcnw of two
active centms or pacemakers one a t either end of the heart. Although
t{his was first postulated by Ling and Locb in 1900 (see Bancroft and
Esterly, 1903) and was accepted by Hecht ( 1 91 8c) experimental proof
came milch later. The evidence may be summarized as follows:
(a) Heating a resting end induces spontnneous activity, that end
becoming dominant. Heating an active end increases the frequency
but heating other parts of the heart usually only alters t h e amplitude of
beat (Skramlik, 1026a,h ; Krijgsman and Krijgsman, 1957 ; Kriebel,
1968s).
(b) Hearts ligatured in the middle rontinucb to beat from both ends
towards the centre, and similarly if the heart is cut in t w o (Schultzc,
1901 ; Hunter, 1903 ; Krijgsman, I
(c) By the use of czuction electrodes attached to either cnd of the
; Kriebc*l. 19fWa).
IVAN GOODBODY
claimed thcit, t,here is a reliiy centrr in the middle dividing the heart
functionally into two pclrte. 1 hnvc ~ l s o observed an apparent relay in
the heart of Corelln rcrillmerinna hiit it is most likely, as suggested by
Hecht (1918c), that it is drir to a shifting of the position of the raphe
and this givcs a fiilse imprcwion of the existence of such n centre.
Reversal of the hetrrt may takc plticc. immediately without, any pausc,
there may be a pnuw of varying duration between opposing waves,
or the two opposing waves may momentarily collide at the centre of the
heiirt beforcl the new wave comes to dominate the other.
The peristaltic wave of cotitrartkm forces blood out of the heart but
in a valveless system it is not easy to see how diastolic filling of the
heart is achieved nnd what prevents backflow through the system. In
the absence of elastic fibres or other attachments there must be other
mechanisms for refilling the Iieert. If the pericardium is punctured the
heart immediately swells iitdicating that it must normally be held
under pressure by the pericardial fluid. Skramlik (1929) was the fist to
point out that presRure in the periclardial fluid was necessary for proper
functioning of the heart and this wns later confirmed by Benazzi (1935).
Skramlik determined that the optimum pressure in the pericardium
was 2 cm water but Kriebel (1968a) found that the optimum is 5 cm
water. Kriebrl also pointed out that this pressure is responsible for the
production of >I contraction valve by forciag the wall of the heart into
the venous ostiuni. As pressure rises in the circulatory system the
venous ” prcssure comes to e x c ~ ~ e d
the pericardial pressure and forces
open the “ virlve ” and refills the heart.
L C
C . Pworrt aker act ivily
l‘hc rhyt hmir alteration of hetirt beat suggests the existcnw of two
active centms or pacemakers one a t either end of the heart. Although
t{his was first postulated by Ling and Locb in 1900 (see Bancroft and
Esterly, 1903) and was accepted by Hecht ( 1 91 8c) experimental proof
came milch later. The evidence may be summarized as follows:
(a) Heating a resting end induces spontnneous activity, that end
becoming dominant. Heating an active end increases the frequency
but heating other parts of the heart usually only alters t h e amplitude of
beat (Skramlik, 1026a,h ; Krijgsman and Krijgsman, 1957 ; Kriebel,
1968s).
(b) Hearts ligatured in the middle rontinucb to beat from both ends
towards the centre, and similarly if the heart is cut in t w o (Schultzc,
1901 ; Hunter, 1903 ; Krijgsman, I
(c) By the use of czuction electrodes attached to either cnd of the
; Kriebc*l. 19fWa).