^rODE OF ACTION OF DIGITALIS. 69 



This question lias generally been limited to the mode in 

 %vhich it affects tlie heart, and the two great theories on this 

 point are — (1) that of Traube,* who thinks that digitalis 

 exerts its influence on the heart through the regulatory (vagus) 

 and musculo-motor system of nerves ; and (2) that of Dybkow- 

 sky, Pelikan, and Kolliker, that it exerts its action on the 

 regulating and motor apparatus, contained in the heart itself, 

 without the intervention of the vagi. Traube at first proposed 

 the theory that digitalis (1) first stimulated the regulatoiy 

 nerves, (2) paralysed them, and (3) paralysed the musculo- 

 motor nerves. The musculo-motor nerves are the cardiac 

 ganglia, which can of themselves carry on the rhythmical 

 movements of the heart ; but these are aided by the sympa- 

 thetic, as, according to the theory of Von Bezold, the cardiac 

 ganglia originate continuous excitations, which, meeting with 

 constant resistance in the cardiac nerves, are only able to over- 

 come it periodically, and then to act on the muscular tissue. 

 To these ganglia two sets of fibres pass from the central nervous 

 masses — " One set reaches the heart partly through the cervical, 

 and partly through the dorsal and lumbar portions of the 

 sympathetic cord. The latter fibres originate in the medulla 

 oblongata, and descending to the cervical, and to some extent 

 through the dorsal and lumbar parts of the spinal cord, emerge 

 at many different points to unite with the sympathetic nerve. 

 The function of all these fibres consists in conveying an exciting 

 influence from the medulla to the heart, so that the resistance 

 in the cardiac nerves is more frequently overcome, and the 

 heart beats more vigorously and with greater rapidity. The 

 second set of fibres, when acting, increase the resistance, and 

 they run in the vagi, and probably also originate in the 

 medulla. When strongly excited they can increase the amount 

 of resistance to so great an extent that it becomes superior to 

 the combined influences of the exciting system of the medulla 

 oblongata and of the motor system in the heart itself. After 

 a short interval it diminishes, and the successive discharges 

 of the automatic centres can then reach the heart, though 

 ^after somewhat longer pauses. By galvanizing the vagus 



* Tear Book Sydenham Society, 18G2, p. 453. 



