ix CARDIAC MUSCLE AND NERVES 333 



respiration in curarised animals, the heart beat longer when tin- 

 vagi were intact than when they had been previously divided. 

 BroNvn-Sequard found on bleeding two rabbits, in one of which the 

 vagus had previously been excited, in the other not, that asphyxia 

 and eventual arrest of the heart were produced more rapidly in 

 the second than in the first. Konow and Stenbeck stated that 

 the rabbit's heart in situ, but completely isolated from the central 

 nervous system, beat for a shorter time, in consequence of asphyxia, 

 than when the vagi were left intact and the spinal cord destroyed. 

 Lastly, the anabolic action of the vagus was confirmed by the 

 nutritional', disturbances that occur in cardiac muscle some time 

 after the division of these nerves. Eichhorst observed in birds, 

 and Wasilieff in rabbits, that the division of the vagi resulted in 

 a certain degree of fatty degeneration of the myocardium. The 

 results obtained by Fantino and Timofeew were, however, more 

 convincing. The former confined himself to cutting one vagus, so 

 that the operated animal remained alive for a longer period. 

 After killing this animal he found nothing remarkable at the post 

 mortem, except the atrophy and non-fatty degeneration of the 

 muscle cells, localised in various regions, according as the rio-ht or 



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left vagus had been divided. Timofeew divided the right vagus 

 below the recurrens, and the left eight days later. The animal only 

 survived the second operation three to five days. Death ensued 

 from adynamia corclis, owing to degeneration of the cardiac 

 muscle, induced bv the failure of the anabolic action of the va*nis. 



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The value of these positive data cannot lie impaired by the 

 negative results obtained on the frog by Bidder and King, since 

 the metabolism of these animals is so sluggish, that they could 

 survive inanition for many months. 



XI. We must next investigate the processes by which the 

 systolic and diastolic nerves of the heart regulate the cardiac 

 rhythm. It has long been known that the heart sends information 

 to the nerve centres of all modifications in its functions, but the 

 study of its afferent nerves is more recent. While investigating 

 the physiological function of the different branches of the cardiac 

 plexus in the rabbit (1886) Ludwig and Cyon discovered a branch, 

 which they termed the depressor nerve. It arises, as shown in 

 Fig. 154, from two roots. Its division produces no change in 

 cardiac rhythm, which proves that it is not in tonic excitation. 

 Stimulation of its peripheral end has LK> effect, showing that it 

 contains no afferent fibres. Excitation of the central end lowers 

 arterial blood pressure, and simultaneously retards the beats of the 

 heart. After division of the vagi this last effect is abolished, 

 while the first remains. The slowing of the rhythm must there- 

 fore be a vagus reflex, and the arterial depression a reflex by way of 

 the vaso-dilators. The depression of blond pressure continues after 

 cutting nut both vagi and the ganglion stellatum. Accordingly, 



