546 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



Fig. 228.— Pulse Tracing op the Frog's 

 Heart. (Sanderson.) 



pulsation of the heart the column of mercury sinks in one arm of the manometer, 

 while it rises a corresponding distance in the other, carrying with it the piston, 

 which by means of its pen traces a line composed of a succession of curves on 

 the smoked surface of the revolving drum. The ascending limb of each curve 

 corresponds to the systole of the ventricle, and the descending curve to its 

 diastole (Fig. 228). By irritating the vagus with a weak induction current the 

 heart stops in diastole, a result similar to that obtained in the previous experiment 

 when the line of junction of the auricle and sinus venosus was irritated. This 

 identical result, however, has not been produced by the same mechanism, as may 



be seen if to the serum in the reservoir 

 a few drops of dilute solution of nico- 

 tine be added ; if the vagus now be 

 irritated, no arrest of the heart occurs. 

 The vagus has been paralyzed by nico- 

 tine ; it no longer is able to restrain 

 the heart, which beats faster than be- 

 fore. (When the nicotine is first given 

 the heart is slowed, and then quick- 

 ened, the slowing being due to the first 

 effects of the nicotine on the vagus, 

 irritating it before it paralyzes it.) 

 It would seem that nicotine and atropine have the same action. But it will 

 be remembered that after atropine poisoning it is impossible to stop the heart 

 through electric irritation of the sinus venosus. 



But if the sinus venosus be irritated in the heart which has received the 

 nicotine, it will stop. Therefore, nicotine and atropine must act on different 

 inhibitory organisms. 



If in a frog which has been placed under the influence of nicotine the heart 

 be removed and placed on a watch-glass, it will pulsate regularly. If a drop of 

 saline solution containing a little of the alkaloid muscarine be placed on the heart, 



it ceases to beat entirely, and will remain motion- 

 less. But if while at rest a drop of a solution of 

 atropine be placed in the heart, it will commence 

 to beat again. 



If in two fresh frogs a drop of muscarine 

 solution.be placed on the hearts, immediately they 

 begin to beat more and more slowly, and at last 

 stop in diastole. If into one frog nicotine be in- 

 jected no effect will be observed ; the heart still 

 remains motionless in diastole ; but the injection 

 of atropine into the other frog whose heart was 

 stopped by muscarine will cause it to commence 

 to beat, and it will pulsate as strongly and rhythm- 

 ically as before the operation. If, however, the 

 atropine be injected first, and then the muscarine 

 be applied, the heart will not be stopped. 



It has now been stated that both nicotine 

 and atropine render the heai-t insusceptible to 

 irritation of the vagus, but that irritation of the 

 sinus venosus will stop the heart in nicotine 

 poisoning, but not in atropine poisoning There- 

 fore some part of the cardiac inhibitory apparatus 

 escapes in nicotine poisoning which is paralyzed 

 by atropine. 



In the above diagrammatic sketch of the arrangement of the cardiac 

 ganglionic apparatus, proposed by Schmiedeberg (Fig. 22U, M). is the main motor 

 ganglion acting on the muscular fibres of the heart by means of radiating fibres. 

 It is regulated by an intermediate apparatus represented by the dotted lines, on 

 the one side by the inhibitory ganglion, I, connected again with an intermediate 

 apparatus with the vagus nerve, and on the other side by the accelerator ganglion, 

 Q, connected in the same manner with the accelerator nerves. According to 

 this arrangement, nicotine is supposed to paralyze the fibres intermediate between 

 the inhibitory ganglion and the vagus nerve, while atropine paralyzes this portion, 



Fig. 229. — Diagram of the 

 Hypothetical Nervous 

 Apparatus of the Heart. 

 (Lauder-S runton. ) 



M. motor ganglion ; I, inhibitory 

 ganglion ; Q, accelerator ganglion ; V, in- 

 hibitory extra-cardiac nerves : S, acceler- 

 ator extra-cardiac nerves. The interme- 

 diate apparatus of Schmiedeberg is 

 represented by the dotted lines. 



