. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine . the cardio-inhibitory cen-ter ; second, through the sympathetic (motor) fibers in thevagus itself : and, finally, through fibers with similar actionin the sympathetic system, usually so called. The share taken by these factors is certainly variable in dif-ferent species of animals, and it is likely that this is true of thesame animals on different occasions. It is also conceivable,and indeed probable, that they act together at times, the inhibi-tory action being diminished and the augm
. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine . the cardio-inhibitory cen-ter ; second, through the sympathetic (motor) fibers in thevagus itself : and, finally, through fibers with similar actionin the sympathetic system, usually so called. The share taken by these factors is certainly variable in dif-ferent species of animals, and it is likely that this is true of thesame animals on different occasions. It is also conceivable,and indeed probable, that they act together at times, the inhibi-tory action being diminished and the augmentor influence in-creased. THE HEART IN RELATION TO BLOOD-PRESSURE. It is plain that all the other conditions throughout the cir-culatory system remaining the same, an increase in either theforce or the frequency of the heart-beat must raise the blood-pressure. But, if the pressure were generally raised when theheart beats rapidly, it would fare ill with the aged, the elasticityof their arteries being usually greatly impaired. As a matter offact any marked rise of pressure that would thus occur is pre-. >w~-s Fig. 218 —Tracing from a rabbit, showing the influence of cardiac inhibition on blood-pressure. The fall in this case was very rapid, owing to sudden cessation of theheart-beat. The relative emptiness of the vessels accounts for the peculiar char-acter of the curve of rising blood-pressure (Foster). vented as a rule, and in different ways, as will be seen ; but, sofar as the heart is concerned, its beat is usually the weaker themore rapid it is, so that the cardiac rhythm and the blood-press-ure are in inverse proportion to each other. By what method is the hearts action tempered to the condi- THE CIRCULATION OF THE BLOOD. 261 tions prevailing at the time in the other parts of the vascularsystem ? The matter is complex. The effect of vagus stimulation onthe blood-pressure is always very marked, as would be supposed. As seen in the tracing, the beats, when the heart c
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