968 PHYSIOLOGY 



also an increase in the flow through the coronary arteries, but it is im- 

 possible with the highest attainable percentages oi carbonic dioxide in the 

 blood to produce such an increase in the coronary flow as is observed during 

 asphyxia. The dilatation of the coronary vessels which occurs in the latter 

 condition must therefore be ascribed to non-gaseous metabolites produced 

 by the contracting muscle. Thus the heart contains in itself a mechanism 

 for increasing the flow of blood through its tissues whenever this becomes 

 inadequate and the muscle is suffering for lack of oxygen. Mechanical and 

 physiological factors thus co-operate in providing the most important muscle 

 in the body with oxygen sufficient for its needs. 



If a coronary artery be ligatured, the heart very often beats for one or 

 two minutes with unimpaired force, then a beat is dropped occasionally, 

 and very shortly afterwards the heart stops altogether and the blood- 

 pressure falls to zero. On inspection, of the heart immediately after the 

 blood-pressure has fallen, its muscular wall is seen to be in a state of fibrillar 

 contractions, or ' delirium cordis.' All the strands of muscle fibres are 

 contracting more or less rhythmically, but the rhythms of no two parts 

 coincide, so that the heart dilates and is incapable of carrying on the circula- 

 tion. It is probably in this way that sudden deaths occur in cases where 

 the coronary arteries are diseased or calcified. In such cases a man may 

 drop down dead, having previously show r n no symptoms of heart mischief. 



Delirium cordis may be explained as the result of block, produced by 

 interference with the nutrition of a large part of the heart- wall. The con- 

 tractile wave arriving at this part, in some directions will not spread at all, 

 in others will spread at a lower rate, so that different parts of the heart 

 receive the impulse to contract at different times and a state of inco- 

 ordination results. The same condition can be produced by freezing the 

 apex of the ventricle, so causing a block, or by stimulating the surface of the 

 ventricle at a rate which is greater than can be taken up by the ventricle as 

 a whole, as, e.g., by tetanising currents. Such a condition in the higher 

 animals, as the dog and man, is practically irrecoverable, although in the 

 rabbit, and very rarely in the dog, it is sometimes possible to bring the heart 

 back to a state of rhythmic contraction by kneading it rhythmically. 



According to Mines delirium cordis is susceptible of a simpler explanation. This 

 condition is easily brought on in the mammalian heart by stimulation of its surface by 

 strong f aradic currents. The effects of increased frequency of contraction on the heart 

 muscle is to decrease the rate of propagation and to decrease the length of the wave 

 of excitation. Ordinarily in the naturally beating heart the wave of excitation is so long 

 and spreads so rapidly, that it excites the whole of the ventricle long before it has 

 ceased in any one part. When, however, the muscle is stimulated more frequently the 

 wave becomes slow and short, so that more than one wave can exist at one time in a 

 single chamber. The main factor then in the production of delirium cordis after 

 obstruction of the coronary artery would probably be a diminished rate of conduction 

 through the affected part, 



