1912.] 



The Action of Adrenin on Veins. 



197 



that a negative result is likely to arise when the muscle of the vein is 

 subnormally excitable to electrical stimulation. 



In the inferior vena cava we have on no occasion been able to induce 

 rhythmic contractions. The rings of the inferior vena cava have always 

 responded by simple non-rhythmic contraction, as shown in fig. 5. 



These experiments are being continued, and extended to the action of other 

 drugs. 



1. The action of adrenin upon ring preparations of veins remote from 

 the heart is to diminish their calibre, as in the case of arteries. They, there- 

 fore, probably contain venoconstrictor nerve fibres from the thoracico-lumbar 

 sympathetic system. 



2. The action of adrenin on quiescent rings from the superior vena cava 

 near the heart is to cause them to beat rhythmically and powerfully. 



3. (a) The accelerator-augmentor nerve supply of the heart, and (b) the 

 rhythmically contractile tissue, extend up the superior vena cava for at least 

 6 — 8 mm. from the veno-auricular junction in the heart of the sheep. 



4. The induction by adrenin of rhythmic contraction in the quiescent 

 superior vena cava seems, on the whole, in accordance with the myogenic 

 theory of mammalian heart rhythmicity. 



Fig. 5. 



Summary. 



