Page:The Harveian oration 1905.djvu/84

 central nervous system; and of the reflex or other factors which are liable to excite cardiac sensory or motor disturbances.

At the present time the so-called "myogenic" doctrine is generally accepted in relation to the heart, namely, that the cardiac movements are automatic, and due to an inherent power of contraction belonging to its muscular fibres. Gaskell sums up the functions of these fibres as rhythmicity, excitability, contractility, conductivity, and tonicity. These inherent functions enable the heart to beat and keep up the circulation without any nervous assistance. Gaskell's investigations demonstrated, however, that some of these functions are more highly developed in certain portions of the heart than in others, and that each part has a special rhythm of its own, due to a morphological difference in structure, according as the muscular fibres approach to ordinary striated muscle in appearance, or are actually striated, or of a more or less embryonic character.

According to the view just indicated, the heart does not possess any motor nerves in the ordinary sense of the term, the vagus and sympathetic merely controlling and modifying the cardiac action as regards rapidity, force, rhythm, or in other respects. Their connection with the spinal nerves explains the superficial phenomena associated with angina pectoris.