322 PHYSIOLOGY CHAP. 



to thrust a needle into this spot in order to produce a fatal 

 delirium of the heart, while any number of punctures at other 

 points of the ventricle had no effect on the co-ordinated contrac- 

 tions. The trend of recent evidence in favour of the neurogenic 

 theory (which has always been upheld by Kronecker for the heart 

 of mammalia also) increases the presumption for this interesting 

 hypothesis- of a co-ordinating, ganglionic centre for cardiac rhythm. 



VIII. Admitting that the rhythmicity of the heart depends 

 on the automatic and reflex excitability of its intrinsic ganglion 

 system, it follows by exclusion that the extracardiac nerve plexus 

 through which the heart is brought into relation with the cerebro- 

 spinal axis can merely exert a regulatory function upon the 

 rhythm, modifying it in accordance with varying external 

 circumstances and the temporary needs of the body. We must 

 now investigate the nature of this regulation of cardiac movements 

 as exercised by the nervous system. 



At the Congress of Italian Naturalists at Naples (September 



FIG. 144. Inhibitory effect of electrical excitation of frog's vagus. (Waller.) Thp pa 



lation is marked on the abscissa by an electric siimal. At the close of excitation the beats 

 become larger. 



1845) the brothers Weber communicated the results of certain 

 experiments which they had undertaken on the effect of stimulating 

 the vagus by tetanising induction currents. To their surprise 

 they obtained neither acceleration nor reinforcement of the beats 

 >/ of the heart, but found they were slowed, or arrested in_diaatole. 

 Stimulation of the intact vagus or its peripheral trunk produced 

 the same result in all classes of vertebrates (Fig. 144). In the 

 frog the excitation of the nerve centres from the optic lobes to the 

 tip of the calamus scriptorius had the same effect. This was a 

 discovery of capital importance, which cleared the way for a vast 

 number of other observations. Budge discovered the same facts, 

 independent of the Webers, and almost at the same moment, but 

 declared himself unable to decide whether the arrest of the heart 

 was due to a cardiac tetanus, as he was then inclined to believe, 

 or to a temporary paralysis of the heart (for which he subsequently 

 concluded on becoming acquainted with the Webers' communica- 

 tion). 



Three different views have been advanced in explanation of this 

 phenomenon : that of the Webers, who regarded the vagus nerves 

 as the restrainers of the heart ; that of Budge, which was imme- 

 diately accepted by Schiff and at a lator time by Moleschott, to the 



