320 INHIBITION AND AUGMENTATION. [BOOK i. 



ganglia onwards they are non-medu Hated fibres. Now we cannot 

 by experiment detect any difference between the augmentor action 

 of the medullated fibres running from the spinal cord to the ganglia 

 and that of the non-medullated fibres running from the ganglia to 

 the heart. By analogy we may infer that the inhibitory fibres are 

 the same in action before and after they become connected with 

 the ganglionic cells within the heart. These cells do not furnish 

 the inhibitory mechanism. Moreover there is evidence that 

 atropin in preventing inhibition does so by producing some change 

 either in the muscular fibres themselves or in the ultimate nerve 

 endings. At present we can make no satisfactory statement as to 

 exactly how either inhibition or augmentation is brought about. 



As to the part however played by the ganglionic cells within the 

 heart in reference to inhibition or augmentation, we may call to mind 

 the fact that stimulation of say one of the cardiac nerves, carrying 

 augmentor or inhibitory fibres leads to augmentation or inhibition 

 of the work not of any particular part of the heart, but of the 

 whole heart ; and as we have already urged, the ganglia probably 

 act as distributors of impulses. They may also in addition have 

 an important work in maintaining the nutrition of the nerve fibres, 

 they may have an important trophic function. 



We have seen that both inhibition and augmentation may 

 affect on the one hand the rhythm, and on the other hand the 

 force of the heart beat. We cannot at present explain this double 

 event. It may be that there are in each case two sets of fibres, 

 one bearing on the rhythm, the other on the force of the contrac- 

 tions ; this is the simpler explanation, but we have as yet no 

 adequate proof in support of it, and other explanations seem 

 possible. 



One other point is worthy perhaps of attention. We have seen 

 that inhibition may be followed by a phase of increased activity, 

 and that on the whole the heart is strengthened rather than 

 weakened by the process, while on the other hand augmentation is 

 followed by depression and the process is -distinctly an exhausting 

 one. Hence whatever be the exact mechanism of inhibition and of 

 augmentation, whatever be the particular elements of the cardiac 

 structures which furnish the one or the other, augmentation means 

 increased expenditure, inhibition means a lessened expenditure, of 

 energy on the part of the muscular tissue of the heart. Whatever 

 the manner in which the respective fibres act, the effect of the 

 activity of the augmentor fibres is to hurry on the downward, 

 catabolic changes of the cardiac tissue, while that of the inhibitory 

 fibres is an opposite one, and we may probably say that the latter 

 assists the constructive, anabolic, changes. 



Other Influences regulating or modifying the Beat of the Heart. 



162. Important as is the regulation of the heart by the 

 nervous system, it must be borne in mind that other influences 



