ACTION ON THE HEART. 49 



believe we cannot avoid tlie conclusion that it exerts a slovvin 



o 



action directhj on the heart. 



In poisoning by digitalis the force of the pulse bears no rela- 

 tion to that of the heart's impulse ; for while the latter is strong 

 and hammering, the former is small, thready, and nearly imper- 

 ceptible. Marey* gives this law, " The force of the pulse is not 

 in correspondence with the energy of the ventricular contrac- 

 tion, but is regulated by the state of the circulation in the 

 ultimate ramifications of the vascular system." The force of 

 the pulse increasing with the arterial tension and diminishing 

 along with it, the weak pulse that occurs in digitalis poisoning 

 is due to the low tension : and this, again, as we shall see 

 hereafter, probably depends on the relaxation of the capillary 

 system, and the rapid transit of blood through it. 



On the Heart. — Having seen that digitalis exerts a primary 

 influence on the heart, the question now arises, What is this 

 action ? And, first, as to its force. Does digitalis weaken the 

 muscular power of the heart ? Does it increase it ? or does it 

 do neither, but simply lessen the number of pulsations, either 

 by diuiinishing its irritability, and so rendering it less sensitive 

 to the stimulus of the blood, or by increasing the power of the 

 regulating part of the nervous system ? 



Very different opinions have been held on these points by 

 different authors. Stanniusf says, that after the injection of a 

 strong dose of digitalis, there is at once a surprising feebleness 

 of the cardiac pulsations, which soon changes into paralysis of 

 this organ, at first partial and then complete : and this he attri- 

 butes to paralysis of its muscular contractility, rather than to 

 any affecrion of its nervous arrangements. 



. Kolliker,J Dybkowsky, and Pelikan hold a similar view. On 

 the other hand, many observers have been inclined, by clinical 

 observation and physiological experiment, to think that digitalis 

 acts rather by increasing the power of the heart ; and that it 

 causes death not so much by paralysis as by spasmodic contrac- 

 tion. Among others who have held this doctrine of stiniulatiou 



* Marey, Physiol. Med. de la Circ. de Sang, p. 235, 

 t Staiinius, quoted by Homolle and Queyenne, p. 234. 

 X Carpenter's I'hysiology, p 229. 



