80 STANNIUS'S EXPERIMENT. 



as a rule the ventricle begins at once to beat again, whilst the auricles remain in 

 the condition of diastolic rest. [Thus the sinus venosus and ventricle continue to 

 beat, while the auricle stands still, but the two former no longer beat with the same 

 rhythm, the ventricle usually beats more slowly, as is shown in fig. 58, 2, by the 

 large zig-zags.] 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. 



Theoretical. Various explanations of these experiments have been given : (a) Remak's 

 ganglion in the sinus venosus 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 

 tiret, 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 (Hcidenhain). [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 adminis- 

 tration 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, or by the action of a constant 

 current of moderate strength (Eckhard), the ventricular pulsation at the same time preceding 

 the auricular (v. Bczold, 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 at the same time, the ventricle is withdrawn from the inhibitory influence of the vagus pro- 

 duced 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 portion 

 of the ganglion in relation with it. (b) According to another view, both Remak's (a) and 

 Bidder's ganglia (b) are motor centres, but in the auricles there is in addition an inhibitory 

 ganglionic system (c) (Bczold, Traube). Under normal circumstances a + b is stronger than c, 

 while c is stronger than a or b separately. If the sinus venosus be separated it beats in virtue 

 of a ; on the other hand, the heart rests because c is stronger than b. If the section be made 

 at the level of the auriculo-ventricular groove, the auricles stand still owing to c, while the 

 ventricle beats owing to b. 



(2) If the ventricle of a frog's heart be separated from the rest of the heart by 

 means of a ligature, or by an incision carried through it at the level of the 

 auriculo-ventricular groove, the sinus and atria pulsate undisturbed as before 

 (Descartes, 1644), but the ventricle stands still in diastole. A single local stimulus 

 applied to the ventricle is responded to by a single contraction. If the incision be 

 so made that the lower margin of the auricular septum remains attached to the 

 ventricle, the latter pulsates. Even the ventricles of a rabbit's heart, when separated 

 with a part of the auricles in connection with them, pulsate (Tiger stedt). 



[Gaakell's Clamp. Gaskell uses a clamp, regulated by a millimetre screw, to compress the 

 heart, and^thus to obstruct the passage of impulses from one part of the heart to the other, or 

 to "block" the way, the pulsations of the auricles and ventricles being separately registered. 

 By compyessing the heart at the auriculo-ventricular groove, the ratio of auricular and ventri- 

 cular beats altera, and instead of being 1:1, there may be 2, 3, or more auricular beats for each 



beat of the ventricle, expressed thus- j , Ij!-, 2; After the heart is fixed by the 



clamp, levers are placed horizontally above and below the heart. These levers are fixed to part 

 of the auricles and to the apex by means of threads. Each part of the heart attached to a 

 lever, as it contracts, pulls upon its own lever, so that the extent and duration of each con- 

 traction may be registered. This method is applicable for studying the effect of the vagus 

 and other nerves upon the heart.] 



(3) Section. A. Fick showed that the process of excitement in the contractile 

 tissue of the frog's heart is propagated in all directions (1874), so that to a certain 

 extent the whole frog's heart behaves like one continuous muscular fibre, thus one 

 transverse cut into the ventricle does not prevent contraction from taking place in 

 the separated parts. Engelmann's experiments also show that if the ventricle of a 

 frog's heart be cut up into two or more strips in a zig-zag way, so that the 

 individual parts still remain connected with each other by muscular tissue, the 



