THE NERVOUS REGULATION OF THE HEART 



167 



of the heart, when cut off from the sinus in which the beat normally 

 originates, needs some time for the development of its automatic power 

 to the point at which an independent rhythm can be maintained. The 

 effects following the second Stannius ligature seem to depend upon the 

 power of the ventricle to develop and maintain an independent rhythm, 

 but the contractions are supposed by some to be started by stimulation 

 of the muscular tissue in the auriculo- ventricular groove by the ligature. 

 Nature of Inhibition and Augmentation. So far we have been dis- 

 cussing the phenomena of inhibition and augmentation as ultimate 

 facts. We have not attempted to go behind them, nor to ask what it 

 is that really happens when inhibitory impulses fall into a heart, which 

 from the first days of embryonic life has gone on beating with a regular 

 rhythm, and in the space of a second or two bring it to a standstill. 

 The question cannot fail to press itself upon the mincl of anyone who 

 has ever witnessed this most beautiful of physiological experiments; 



Fig. 76. Frog's Heart. Sympathetic stimulated (30 mm. between the coils). 

 Temperature 12. Marked increase in force. Only auricular tracing rcpro. 

 duced. Time-trace, two-second intervals. 



but as yet there is no answer except ingenious speculations. The most 

 plausible of these is the trophic theory of Gaskell, who sees in the vagus 

 a nerve which so acts upon the chemical changes going on in the heart 

 as to give them a trophic, or anabolic, or constructive turn, and thus to 

 lessen for the time the destructive changes underlying the muscular 

 contraction. The augmentor nerves, on the other hand, are supposed 

 to exert a katabolic influence, and to favour these destructive changes. 

 And while, according to Gaskell, the natural consequence of inhibition 

 is a stage of increased efficiency and working power when the inhibition 

 has passed away, the natural complement of augmentation is a tem- 

 porary exhaustion. It is very risky, however, to rely, as Gaskell did, 

 upon a supposed change of sign in the electrical effects during vagus 

 stimulation, and the only chemical test to which the theory has been 

 subjected, the comparison of the oxygen consumption of the heart during 

 and in the absence of inhibition, is adverse to it. The amount of oxygen 

 used up relatively to the functional activity of the heart as measured by 

 the product of the frequency of the beat and the maximal increase of pres- 

 sure caused by it, is not increased by stimulation of the vagus (Rohde). 



