THE CIRCULATION. 253 



STANNTUS'S EXPERIMENT. If the sinus venosus of the frog's 

 heart be separated from the auricles by the application of a ligature, 

 then the auricles and ventricles will remain quiet in diastole, while the 

 veins and the remainder of the sinus continue to beat. If a second 

 ligature be applied at the junction of the auricles and ventricle, the 

 usual sequence is for the ventricle to begin to beat again while the 

 auricles continue to remain in their diastolic rest. Though the two, 

 sinus venosus and ventricle, continue to beat, their motion is not 

 rhythmical, the ventricular movements being considerably slower. In 

 every case the quiescent portion can be made to give single contrac- 

 tions by stimuli, either mechanical or electrical. Thus, when the 



A B 



Fig. 76. Schema of Ligatures of Stannius. 



A. Ligature below the auriculo-ventricular groove (L) ; the sinus venosus 

 (3) and the auricles (1) continue to beat, but the apex of the isolated ventricle 

 is arrested. 



B. Ligature of L to sinus (3), which continues its rhythmical beats; 1 and 

 2 are arrested in diastole (seventh experiment of Stannius). 



C. After the ligature (L) as in B, a second ligature (L') is placed around 

 the auriculo-ventricular groove; the ventricle, which was originally arrested, 

 after some rhythmical contraction, is again arrested (tenth experiment of 

 Stannius). 



ventricle remains quiet after the first ligature, it may be made to give 

 single contractions by pin-pricks. 



There are two explanations of the effects of Stannius' ligature, 

 known as the nerve theory or neurogenic theory of the cause of the 

 heart-beat, and the muscle theory or the myogenic theory (sinus 

 theory) of the heart-beat. I shall first take up the neurogenic theory. 



Neurogenic Theory. To explain the experiment of Stannius it 

 has been asserted that Remak's and Bidder's ganglia are motor and 

 von Bezold's is inhibitory; that the motor influence of Remak's and 

 Bidder's is greater than the inhibitory influence of von Bezold's ; hence, 

 in the absence of all ligatures, the heart beats. That the motor power 

 of Bidder's is less than the inhibitory power of von Bezold's ; conse- 



