PAROXYSMAL IRREGULARITY OF THE HEART 1 5 



rare or only seen in moribund cases. We are therefore disposed to 

 attribute the condition observed in our experiments to reflex influences 

 on the heart. These impulses must reach the heart either by the vagus or 

 by the sympathetic fibres. And, as a matter of fact, we have observed 

 one instance in which vagus stimulation was followed by delirium. In 

 this dog, the heart was peculiarly irritable and much accelerated. The 

 myocardiograph had been attached to the right ventricle and auricle, and 

 a tracing was being taken. The effects of electrical stimulation of one 

 vagus in the neck were being demonstrated, and the usual response 

 followed — arrest of the auricle and ventricle in diastole. But when the 

 current was shut off, the heart, instead of returning to its normal rate, 

 passed into fibrillary contractions in both auricle and ventricle. This is 

 the only instance in which we have seen the unpoisoned heart affected in 

 this way from the cessation of inhibition. In several experiments in 

 which the irritability of the heart was exaggerated by large doses of 

 members of the digitalis series or of barium, section of the vagus led 

 immediately to fibrillary contractions in the auricle and ventricle. 



As has been stated, we have obtained no tracings of the pulse in 

 dogs in which the heart passed into auricular delirium during the 

 operations. The phenomenon is a rare one in our experience, although 

 we have observed it sufificiently often to have no doubt as to its 

 occurrence, and as to its association with the operation. In several 

 experiments the. pulse was recorded during the operation by means of 

 Von Frey's or Hiirthle's tonometer, attached to the carotid artery, and 

 the anaesthesia was maintained at a point at which, while pain was absent, 

 the reflexes were retained as far as possible. In none of these, however, 

 was the auricular delirium developed, although the pulse was much 

 accelerated ; occasionally intermissions of the pulse occurred of the 

 auricular type, indicating perhaps a tendency to fibrillation. The 

 acceleration was very slight, or entirely absent in experiments in which 

 atropine had been previously injected in quantities sufficient to paralyse 

 the cardiac vagus. The acceleration in dogs without atropine was thus 

 due for the most part to lessened vagus tone, from the centre being 

 inhibited by impulses from the seat of operation. It seems likely that the 

 auricular delirium observed in rare cases in dogs during the operation is 

 similarly to be explained by the disappearance of inhibition ; the auricles 

 must in these cases, however, be in some quite unusual condition of 

 irritability. (109) 



