CIRCULATION OP THE BLOOD. 543 



the ventricle will again pulsate, but its rhythm will be no longer syn- 

 chronous with that of the sinus. 



In another frog, prepared in the same manner, the heart may be 

 separated from the sinus venosus with a pair of scissors, following the 

 line of the ligature in the preceding experiment, and the result will be the 

 same. Cut off the ventricle, including the auriculo-ventricular groove, 

 from the auricle before it starts spontaneously to pulsate, the ventricle 

 immediately begins to beat ; the same result might have been obtained 

 after ligature as in the first experiment. 



Or, if- this line be irritated with an induction current, taking care to 

 include the sinus in the current, the same result will follow. But in a 

 frog in which x^o OI " a grain of atropine has been injected irritation with 

 the electric current will have no effect ; while if the first experiment is 

 repeated, by ligating this line, the heart will stop as before. 



What inference can be drawn from these experiments ? It has been 

 stated that the ganglion of Remak, a motor ganglion, is situated at the 

 opening of the inferior vena cava, that is, in the sinus venosus ; also that 

 the inhibitory ganglion of Ludwig is in the interauricular septum, and the 

 motor ganglion of Bidder in the left auriculo-ventricular septum. We 

 may assume that Remak's ganglion is an automatic motor centre, i.e., 

 "a ganglionic centre in which energy tends to accumulate and discharge 

 itself in the form of motion at regular intervals, the length of which varies 

 with the resistance to the discharge and with the rapidity of the accumu- 

 lation," the physiological grounds for this assumption being as follows: 

 The succession of acts which make up a cardiac revolution distinctly 

 start in the sinus ; this is the only portion of the heart that contracts 

 independently, and electric excitation of this centre induces increased 

 frequency of contraction of the whole organ. By separating the heart 

 from the sinus venosus, either by ligature or by amputation with the 

 scissors, we not only remove the heart from its main motor centre, but 

 also irritate the inhibitory centre, and so cause arrest of the pulsation 

 of the heart, while the sinus containing the motor centre goes on con- 

 tracting as before. After a few minutes, however, the inhibitory effect 

 induced through irritation passes off, and then the motor ganglion at the 

 base of the ventricle starts the heart again. So, when, without waiting 

 for the inhibition to pass off, we remove the ventricle from the auricles, 

 the motor ventricular ganglion is released from its inhibition and starts 

 the heart again. The effect is somewhat different, however, when we 

 irritate this line with electricity ; then the stoppage is due alone to the 

 inhibitory action of the ganglion, and when this passes off the heart 

 pulsates. So, when this inhibitory ganglion is paralyzed with atropine, 

 electric irritation is powerless to stop the heart, while ligature by re- 

 moval of the heart from its main motor centre prevents pulsation. 



