194 



Messrs. J. A. Gunn and F. B. Chavasse. [Dec. 13, 



found that stimulation of the sciatic nerve in the cat and rabbit produced 

 visible contraction of the superficial veins of the hind limbs. 



(b) Veins Near the Heart. 



Considerable interest attaches to the action of adrenin on the great veins 

 near the heart. It has long been known that in the mammal the great 

 veins near the heart, which correspond in some ways at least to the sinus 

 venosus in the frog, beat rhythmically with the heart proper. One of us 

 has on previous occasions made unsuccessful attempts to obtain a spon- 

 taneously contracting ring preparation of the superior vena cava of the cat 

 and rabbit. A renewal of this endeavour with the larger rings from the 

 sheep and bullock has been equally unsuccessful, though it is not suggested 

 that this may not yet be accomplished. 



What we believe to be a phenomenon of considerable interest and import- 

 ance is that such a quiescent ring preparation of the superior vena cava near 

 the heart can be made to beat vigorously and rhythmically by the action of 

 adrenin. 



For these experiments the venae cavae were removed along with part of 

 the auricle, so that the distance of the ring from the auricle could be 

 measured accurately. 



Fig. 3 shows the effect of adrenin, 1 in 20,000, on a ring preparation of the 

 superior vena cava of a sheep, 6 mm. distant from the angle of its junction 

 with the auricle. The kind of effect produced by adrenin on this venous 

 ring is exactly like that produced by it on the whole heart. Though it 

 cannot be postulated with absolute certainty in the case of the quiescent 

 tissue, inspection of the tracing leaves little room for doubt that adrenin 

 augments and accelerates the contractions of the ring. 



In the first place, therefore, this method of experiment affords evidence in 

 favour of the view that the augmentor-accelerator nerve supply of the heart 

 extends for some distance up the superior vena cava. 



Secondly, it throws some light on the origin of the rhythmicity of the 

 heart. The ring of the superior vena cava is quiescent. (This is established 

 not only by the absence of movements of the lever, but also by observation 

 of the ring in a strong light.) Adrenin almost immediately induces powerful 

 rhythmic contractions. The action of adrenin is a continuous stimulus to 

 which the muscle responds by a discontinuous (rhythmic) contraction. 



Now the researches of Lewandowski, Langley, Elliott, Dale, and others 

 have established with an unusual degree of certainty that adrenin acts on 

 the myo-neural junctions of the thoracico-lumbar sympathetic system, and 

 that its action is confined to these. Unless, therefore, the action of adrenin 



