THE HEART 47 



however, less than on the thin-walled veins. When the ventricle 

 begins to contract, it can be shown that the pressure and 

 velocity in the coronary arteries is increased ; but as the con- 

 traction proceeds, and the muscle, as it were, is being wrung, 

 the coronary vessels are clamped, and the blood in the arteries 

 is driven back on the aorta, while that in the veins is forced 

 onwards to the right auricle. At diastole the coronary arteries 

 at once refill, and, as we have seen above, a further charge is 

 pumped in at the beginning of contraction. Other experiments 

 appear to show that with each systole of the heart the coronary 

 system is emptied towards the venous side, and at each diastole 

 it is filled. 



The effect of occluding the coronary arteries is of the utmost 

 practical interest. If all the arteries be clamped the heart at once 

 stops ; but if the observation be limited to one vessel only, that 

 portion of the ventricle supplied by it ceases to beat. The arrest 

 of the ventricle is a curious condition, giving rise either at once 

 or soon after to the phenomenon known as fibrillar contraction, 

 in which the surface of the heart presents vibrating, twitching, 

 disorderly movements, to which the term delirium cordis has 

 aptly been applied. It is as if each fibre of the heart were 

 irregularly contracting on its own account, independently of its 

 neighbours. 



Fibrillation of the auricles may also be experimentally pro- 

 duced, but the auricles, unlike the ventricles, appear to possess a 

 greater capacity for returning to co-ordinate contraction. Con- 

 siderable attention is now being paid clinically to fibrillation of 

 the auricles, which Lewis* finds is the commonest persistent 

 irregularity exhibited by the human heart, constituting approxi- 

 mately 50 per cent, of all such cases. He has also observed it 

 in the horse, and it is quite likely that it may turn out to be a 

 relatively frequent condition. Though fibrillation of the ventricles 

 means immediate death, fibrillation of the auricles does not. The 

 ventricles are indispensable to the circulation, but the auricles, 

 as we have seen, are practically reservoirs, and without their 

 assistance the ventricles fill by gravity ; in fact, as we have 

 already learnt, under normal conditions the ventricle is nearly 

 full before the auricular systole occurs. Fibrillation of the 

 auricles gives rise to a train of symptoms, sometimes associated 

 with great distress, but not necessarily fatal to life. The cause 

 of this condition will be explained presently. r *j 



The Cause of the Heart-Beat. — It seems incredible that the 

 use of the heart should have remained unknown until the early 

 part of the seventeenth century. Even now some of the chief 



* T. Lewis, M.D., D.Sc, 'Auricular Fibrillation,' Heart, vol. i., No. 4, 

 1910. 



