CONCLUSIONS AS TO THE CARDIAC MECHANISM. 453 



summary of the functional mechanism of the heart as devel- 

 oped in the present chapter: 



1. The nervous supply of the heart is derived from the general 

 motor (sympathetic) and vagus systems. 



2. The general motor plexuses and nerves maintain the nor- 

 mal tonic contraction of the coronaries and other cardiac vessels 

 and insure distribution of the blood among the muscular elements. 



3. The vagal plexuses and nerves incite and govern the rhythm 

 of the heart, reducing or increasing its beats. 



4. Increase of the vagal vibratory rhythm (impulses) causes 

 quickening of the heart-beats. 



5. Excessive vibratory rhythm of the vagus (or spinal ac- 

 cessory) causes arrest of the heart-beats: i.e., inhibition. 



6. Reduction of the vagal vibratory rhythm causes, when phys- 

 iological, slowing of the heart-beats. 



7. Reduction of the vagal vibratory rhythm, when pathological, 

 especially when due to adrenal insufficiency, results in quickening 

 and weakening of the heart-beats, through loss of vagal control. 



8. Cessation of the vagal vibratory rhythm (as after division 

 of the vagus on both sides) is followed by marked quickening and 

 weakening of the heart-beats, through loss of vagal control. 



9. The mechanical energy upon which the right heart depends 

 is of two kinds: (1) the contractile action of the adrenal secretion 

 brought to it by the inferior vena cava; (2) the continuous action 

 of the oxidizing substance of the coronary arterial blood upon myo- 

 sinogen formed from granules fi, the latter being derived from the 

 liver. 



10. The adrenal secretion and the granules (3 enter the right 

 auricle and the right ventricle with the blood of the vena cava. 



11. The adrenal secretion, owing to its direct action on mus- 

 cular tissue, causes the walls of these cavities to contract alternately 

 upon their venous contents and to force a small quantity of the latter 

 into the Thebesian foramina and channels. 



12. This blood then penetrates the interfibrillary spaces of 

 Eenle, i.e., around the bare muscle-cells, and its granules {$ 

 are used by the latter to build up their myosinogen. 



13. As the plasma of the coronary arteries and their terminals, 

 the pericellular capillaries of the muscle- elements, contain oxidizing 



