THE HEART-BEAT IN ITS PHYSIOLOGICAL RELATIONS 151 



tion between the ventricles and auricles has continued after destruction 

 of the A-V bundle, while sometimes co-ordination has been upset by 

 lesions not affecting the bundle. 



Fibrillary Contraction. In the case of the warm-blooded heart a 

 complete breakdown of co-ordination occurs under certain circum- 

 stances, producing the phenomenon known as fibrillary contraction, 

 or delirium cordis, a condition in which each minute portion, perhaps^ 

 each fibre, of the whole heart, or of a portion of it, goes on contract- ' 

 ing in a disorderly manner, quite independently of the rest. The 

 condition is often seen in a heart that has been exposed for some 

 time, particularly in the ventricle, and can be induced by stimulating 

 it with strong induction shocks or by ligation of the coronary 

 arteries. According to the best evidence, the condition is due to 

 the fact that the conductivity of the fibrillating muscle is interfered 

 with so that the contraction wave is prevented from running its 

 usual course. The consequence of this ' blocking ' is that the 

 normal co-ordinated action of the musculature gives place to the 

 confused movement characteristic of fibrillation (Porter, Garrey). 

 There is no reason to believe that fibrillary contraction is connected 

 with the loss of impulses from any special co-ordinating centre, for 

 it is not peculiar to the heart, but is typically seen in the tongue 

 when the circulation after a long interruption is restored. The 

 peculiar ' boiling ' movement is exactly similar to that observed in 

 the heart, probably because the tongue also contains fibres running 

 in several directions. 



The confused fibrillary contractions are quite ineffective for driving 

 on the contents of the heart. Fibrillation of the ventricle is therefore 

 incompatible with life. On the other hand, auricular fibrillation, far 

 from being immediately fatal, is one of the most common of the chronic 

 cardiac disorders in man. It is characterized by extreme irregularity 

 of the pulse, due to the fact that the ventricles are played upon by an 

 irregular stream of impulses from the fibrillating auricles to which they 

 respond as they best can. The auricular wave (a, Figs. 65-67) is absent 

 from the jugular pulse -tracing, and the P wave (Fig. 809), corresponding 

 to the electrical change produced by the normally contracting auricles, 

 is absent from the electrocardiogram. Auricular flutter is a condition 

 which must be distinguished from auricular fibrillation. When a weak 

 stimulus is applied to the auricle of a dog or cat, the auricular beats are 

 greatly increased in frequency up to 300 or 400 a minute. Although 

 the beats are so rapid, they are otherwise normal beats. When the 

 strength of the stimulus is increased, this condition of flutter 

 (Mac William) passes into fibrillation. Auricular flutter is also recog- 

 nized clinically. In the majority of cases the ventricle does not respond 

 to each beat of the auricle, and the arterial pulse is irregular; but each 

 auricular contraction produces its appropriate effect upon the electro- 

 cardiogram and often also upon the jugular tracing (Mackenzie). 



Without entering further into a discussion of the rival hypotheses, 

 we may sum up by saying that for one heart (that of Limulus) the 

 automatism and the rhythmical power have been clearly shown to reside 



