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beat of the heart is clue to an intrinsic rhythmical contractile power of the cardiac muscle, possessed by all parts in greater or lesser degree, but most marked in the venous sinus and auricle, whence a wave of contraction is propagated through the heart, leading the sequence and setting the pace to the other chambers. From this point of view the cardiac ganglia are merely peripheral ganglia of the efferent visceral fibres of the vagus, analogous to those of the visceral system of nerves in general. The heart, however, in its normal relations is not a mere mechanical pump, automatically working so many times a minute and turning out so many gallons of blood per diem in steady and regular flow. The needs of the organism are ever changing, and the heart and vascular system are ever adapting themselves in accordance therewith. There is scarcely an act, or thought, or feeling which does not reflect itself in the rate of the heart and state of the pulse. The explanation of these variations is to be sought for in the relations which subsist between the central nervous system and the heart and blood-vessels. Though to the physiologist this is a
