THE CENTRES OF THE CARDIAC NERVES. 55 



change markedly under the influence of suggestion. Inquiry for 

 cerebral cardiac centres has been made by the methods of cortical 

 excitation. If, by the use of suitable strengths of current, the excita- 

 tion of epileptic fits be avoided, Francois-Franck finds that stimulation 

 of any part of the motor area accelerates the heart when a weak current 

 is employed. On the other hand, a strong current slows the heart. 

 From other parts of the cerebrum the heart can also be influenced. All 

 these cerebral effects are similar to those excited reflexly by stimulation 

 of afferent nerves. The vagus centre maintains over the heart a tonic 

 bridle action, and the question arises as to whether this tonus is kept 

 up reflexly by the constant instreaming of afferent impulses, or whether 

 the centre possesses automatism. 



According to Soltmann and others, vagal tone is not to be found in 

 the new-born animal. 1 On the other hand, pressure on the head of the 

 new-born child slows the pulse, 2 and thus the centre can be reflexly 

 excited. In support of the hypothesis that the tone depends on 

 afferent impulses, the following experiments may be quoted : — 



1. After dividing the cervical spinal cord, the heart is said not to 

 be accelerated by a subsequent division of the vagi. 



2. After section of the splanchnic nerves, and thus diminishing the 

 sensory field from which reflexes are excited, the pulse frequency is 

 increased. 



Neither of these experiments, however, proves that the tone depends 

 on afferent nerves, for the arterial tension is greatly lessened by both 

 operations. In consequence of any great fall of arterial tension, the 

 heart is accelerated. This acceleration may be so great that the 

 frequency is not increased to any further degree by section of the 

 vagi. There can be no doubt that the arterial pressure is one of the 

 most important agencies by which the vagus centre is constantly 

 influenced, and since it is quite impossible to cut off all afferent 

 impulses from this centre, and at the same time remove the influence 

 of the arterial pressure, the automatism of the centre can neither be 

 proved or disproved. The theoretical assumption of such a power is 

 not required. 



After section of both vagi, excitation of the medulla oblongata 

 causes cardiac acceleration. This acceleration takes place after 

 section of the splanchnic nerves, and thus is independent of vaso- 

 constriction and the rise of arterial tension, which normally follows 

 such excitation. A centre for the accelerator nerves is localised in the 

 spinal bulb, and is said to maintain a tonic influence over the heart. 

 Tschirjew, 3 and also Strieker and Wagner, 4 have witnessed, after 

 section of the vagi, a decrease of the pulse rate to take place on 

 excision of the inferior cervical and first thoracic ganglia. It is also 

 affirmed that, after section of the accelerator fibres, inhibition by ex- 

 citation of the vagus can be induced with greater ease than before. 

 The inhibitory effect is likewise obtained more easily after section of the 

 cervical spinal cord. 5 



Since, by the operative procedures of exposing the accelerator nerve, 



1 Jahrb.f. Kinderh., 1877, S. 101. 



2 Engstriim, " Fiirlossningeus inverkan pa fostrets respiration, " Helsingfors, 1889, S. 2-15, 

 eited after Tigersteilt. 



3 Arch./. Physiol., Leipzig, 1877, S. 164. 

 * Wien. ?ned. Jahrb., 1878, S. 370. 



6 Sustschinsky, Untersuch. a. d. physiol. Lab, in Jl r iir:biirc/, 1868, Bd, iii, S. 1*>4, 



