34 GENERAL ACTIONS OF DRUGS 



originating from the medullary centre, and its fibres termi- 

 nating in the heart. 



3. The accelerator apparatus, consisting of the accele- 

 rator nerve — with centres in the cerebrum and medulla — 

 and its fibres passing down the spinal cord to the dorsal 

 nerves ; from thence through the first thoracic ganglion to 

 the sympathetic, and so on to the cardiac plexus, with peri- 

 pheral terminations in the heart. The ganglia in the heart 

 are situated about the auriculo- ventricular groove and at the 

 entrance of the superior and inferior venae cavae, and at the 

 orifices of the pulmonary veins. 



The ganglia have been divided into the inhibitory, 

 connected with the vagus nerve ; the motor ; and the 

 accelerator ganglia; and they are supposed to be influenced 

 by drugs as well as the rest of the mechanism detailed above. 

 Our. knowledge of the functions of these ganglia is imperfect 

 and therefore of the action of drugs on them. 



' The action of drugs on the heart-muscle has been deter- 

 mined by estimating their influence on the lower two-thirds 

 of the apex, which is comparatively free from nerve supply. 



The action of drugs on the inhibitory apparatus is of 

 more importance than that exerted on the accelerator nerve, 

 and we know more about it. Drugs usually affect the roots 

 of the vagus nerve in the centre, or its peripheral termina- 

 tions in the heart, rather than its trunk. The heart is 

 influenced by drugs as follows : 



1. Stimulation of the inhibitory apparatus leads to 

 slowing and weakening of the heart-beats, or to both. 



2. Depression of the inhibitory apparatus results in 

 quickening or strengthening the heart-beats, or both. 



3. Depression of the accelerator apparatus induces 

 decrease in the rate or force of the heart-beats, or both. 



4. Stimulation of the heart-muscle produces increase in 

 the rate or force of the heart-beats, or both. 



5. Depression of the heart-muscle lowers the rate or 

 force of the heart-beats, or both. 



The vagus centre is stimulated by agencies increasing 



