470 OF THE CIRCULATION OP THE BLOOD. 



after section of the Pneumogastrics; but when the large proportion of the Sym- 

 pathetic nerves proceeding to this organ is considered, and when it is also re- 

 membered that irritation of the roots of the upper cervical nerves stimulates 

 the action of the heart through these, we can scarcely doubt that both may 

 serve as the channels of this influence, especially in such animals as the dog, in 

 which the two freely inosculate in the neck. Although there is a difficulty in 

 proving that the Heart's action can be excited or accelerated by irritation of 

 the Pneumogastrics, yet these nerves may serve as the channel of an influence 

 of a very opposite character; for the experiments of MM. Weber have shown 

 that its movements may be immediately arrested by the transmission of the 

 electric current from a rotating magnet, either through the Spinal Cord, or 

 through the Pneumogastrics divided at their origin ; the same irritation, how- 

 ever, applied to a single one of the Vagi, produced no effect. 1 Hence it is ob- 

 vious that the influence of sudden and violent injury to the Cerebro-spinal centres, 

 which induces an immediate diminution or suspension of the Heart's mechanical 

 movements, or even entirely annihilates them, may be conveyed through these 

 trunks, as well as through the Sympathetic system ( 321). 



497. In like manner it may be shown that the Heart's action may be affected 

 by influences transmitted through the Sympathetic system of nerves. There is 

 considerable difficulty in obtaining direct experimental evidence to this effect, of 

 a satisfactory character ; but there is strong reason to believe that the effects of 

 shock may be exerted no less directly through the Sympathetic than through 

 the Cerebro-spinal system ( 321); and that considerable disturbance may ensue 

 from lesions of such parts of it (at least) as are most nearly connected with the 

 heart. Thus a case has been put on record, in which the heart's pulsations were 

 occasionally checked for an interval of from 4 to 6 beats, its cessation of action 

 giving rise to the most fearful sensations of anxiety, and to acute pain passing 

 up to the head from both sides of the chest these symptoms being connected, 

 as it proved on a post-mortem examination, with the pressure of an enlarged 

 bronchial gland upon the great cardiac nerve. 2 It is not less obvious, however, 

 in regard to the principal centres of the Sympathetic system, than with respect 

 to those of the Cerebro-spinal, that in whatever degree the heart's action may be 

 influenced through them, it cannot be dependent upon any power which it derives 

 from them, since it continues after the complete isolation of the organ. And 

 the very difficulty of obtaining experimental evidence of this influence, notwith- 

 standing the extraordinary irritability of the Heart, seems to show that the 

 ordinary movements of the organ are but little dependent upon nervous influence 

 of any kind. The only centres of nervous power, to which, consistently with 

 the foregoing facts, the maintenance of the Heart's action can be attributed, are 

 the numerous ganglia, forming part of the Sympathetic system, which are dis- 

 persed through its substance, but which are brought into connection with each 

 other by communicating fibres. These, it has been surmised, may act as centres 

 of " reflex" action; and may thus keep up the contractions of the heart, after 

 its complete withdrawal from the influence of the Cerebro-spinal and of the princi- 

 pal Sympathetic centres, just as the ganglia contained in the separated segments 

 of the body of a Centipede are centres of movement to the limbs with which 

 they remain in connection. But this hypothesis does not give any real solution 

 to the difficulty; for in every case of true "reflex" action, the movement is ex- 

 cited by a stimulus; and no rhythmical succession of movements can be thus 



1 "Archives d'Anat. Gener. et de Physiol.," Jan., 1846; and "Wagner's Handworter- 

 buch," Art. "Muskelbewegung." 



8 "MullerYArchiv.," 1841, heft iii. ; and "Brit, and For. Med. Rev.," Oct., 1841. It 

 may be surmised that in many cases of angina pectoris, in which no lesion adequate to ac- 

 count for death could be discovered, some affection of the cardiac plexus might have been 

 traced on more careful examination. 



