INHIBITION AND CARDIAC VAGUS 113 



heart to increased rapidity of action until the vagus once 



more controls it. So the accelerator replies to a rapid 



stress, the vagus to a continued one. Tachycardia as a 



morbid condition is probably not always due to abnormal 



alterations in the ' ' pace-maker. ' ' When the organism grows 



weak, and the blood-pressure falls, the cerebral arteries 



and coronary system can only be kept going by increased 



rapidity, which makes up for the small volume of blood 



sent into the aorta at each ventricular contraction. Every 



one who has observed tired and worried workers, forced to 



continue by urgent stimuli, has seen them go through such 



stages. A man who works under pressure with a shovel 



increases his rapidity and decreases his load. Seamen 



tend under similar circumstances to take short ineffective 



pulls on the gear at which they are hauling, and are apt 



to do it in silence without the " pace-maker " of a rhythmic 



song. I may be exposing myself to the ridicule of the 



unobservant if I liken to vagus action the mate's voice 



urging them to use their strength more rhythmically and 



conservatively. But every worker who has toiled under 



stress will be able to recall analogies in his own experience 



which strengthen such an illustration. 



It appears, then, as if the vagus and accelerator fibres 



had no function of very great importance in health, rest, and 



easy normal conditions, although without doubt they make 



minor corrections in the cardiac mechanism at all times. 



The necessity of explaining " inhibition " in the heart thus 



seems only to exist in the laboratory, in the casualty 



ward, or on the operating table. Then the conditions are 



pathological ; the cases are cases of " shock," if shock is 



disruption of united organic action with concomitant effects 



upon the organs by which stability is assured. Such an 



explanation seems in accord with what is known of the 

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