618 
PHYSIOLOGY 
Jack Han, Albany Medical College, N.Y.: 
I'm under the impression that the refractory 
period of a bundle branch system in swine is 
much longer than that of the A-V node. We have 
done some His bundle electrograms, and when 
we stress, say, the A-V conduction system in 
swine, we have found that the level of block is 
below rather than above the His. I am wonder- 
ing if this may explain the unusually long acute 
interval in swine which we have also observed? 
We also find that the fibrillation threshold is 
very much lower in swine than in the dog. This 
may have some relationship to a long acute in- 
terval in swine, too. 
Dr. Hamlin: ^hose are interesting com- 
ments. It is my impression, however, that in all 
species the duration of the longest action po- 
tential is below the A-V junction in the bundle 
of His, or approximately the left or right 
bundles. So I think the pig would be consistent 
with that. 
