100 STANNIUS' EXPERIMENT. 



which lead to the regular alternating action of the various parts of the 

 heart, so that under normal circumstances, we must assume that the 

 action of the heart is governed by the ganglia. 



The chief experiments upon which the above statements are based 

 consist of two classes: (1.) Where the heart is INCISED or DIVIDED; 

 and (2.) where it is STIMULATED DIRECTLY. 



(I.) Experiments by CUTTING and LIGATURING the heart. These 

 experiments have been made chiefly upon the frog's heart. The 

 LIGATURE experiments are performed by tightening and then relaxing 

 a ligature placed around the heart, so that the physiological connection 

 is destroyed, while the anatomical or mechanical connections (con- 

 tinuity of the cardiac wall, intact condition of its cavities) still exist. 

 The most important of these experiments are 



(1.) Stannius' Experiment. If the sinus venosus of a frog's heart 

 be separated from the auricles, either by an incision or by a ligature, 

 the auricles and ventricle stand still in diastole, whilst the veins and 

 the remainder of the sinus continue to beat. If a second incision be 

 made at the auriculo-ventricular groove, as a rule the ventricle begins 

 at once to beat again, whilst the auricles remain in the condition of 

 diastolic rest. According to the position of the second ligature or 

 incision, the auricles may also beat along with the ventricles, or the 

 auricles alone may beat, while the ventricles remain at rest (1852). 



Explanations. Various explanations of these experiments have been given : 

 (a.) Eemak's ganglion in the sinus vinosus is distinguished by its great excitability, 

 while Bidder's ganglion in the auriculo-ventricular groove is less excitable ; in the 

 normal condition of the heart the motor impulse is carried from the former to the 

 latter. If the sinus venosus be separated from the heart, Remak's ganglion has no 

 action on the heart. The heart stops for two reasons first, because Bidder's 

 ganglion alone has not sufficient energy to excite it to action, and because 

 the inhibitory fibres of the vagus going; to the heart have been stimulated by 

 being divided at this point (Heidenhain). [That stimulation of the inhibitory 

 fibres of the vagus is not the cause of the standstill, is proved by the fact that the 

 standstill occurs even after the administration of atropine, which paralyses the 

 cardiac inhibitory mechanism.] The passive heart, however, may be made to 

 contract by mechanically stimulating Bidder's ganglion e.g., by a slight prick 

 with a needle in the auriculo-ventricular groove (H. Munk), or by the action of a 

 constant current of moderate strength (Eckhard), the ventricular pulsation at the 

 same time preceding the auricular (v. Bezold, Bernstein). If the auriculo- 

 ventricular groove be divided, the ventricle pulsates again, because Bidder's ganglion 

 has been stimulated by the act of dividing it; while, at the same time, the ventricle 

 is withdrawn from the inhibitory influence of the vagus produced by the first 

 division at the sinus venosus. If the line of separation is so made that Bidder's 

 ganglion remains attached to the auricles, these pulsate, and the ventricle, rests ; 

 if it be divided -into halves, the auricles and ventricles pulsate, each half being 

 excited by the p'Qrfion^of r the gangKod"*!]. reMtiou.mth it. (6.) According to 

 another view, both R^mak's r (a.) and- Bidder's/ganglia (h.) t are motor centres, but 

 in the auricles"' tifere IP ^n; addition an inhibitory ganglionic system (c.) (Bezold, 

 Traube). TJn^ei- Dorm^cfrcums'tances h^'oik Vtron-ger'tfcefc^: while c is stronger 



