42 



Scientific Proceedings (5 1). 



and ventricles then beat simultaneously. The application of a 

 third clamp at the junction of the inferior vena cava and auricle 

 was followed by reversal of the mechanism which persisted until 

 the animal was killed. 



The occurrence of reversal but once in a series of seven experi- 

 ments has occasioned no surprise. We had surmised that after 

 destruction of the usual pacemaker it would be quite fortuitous 

 should the next most irritable focus lie below the auricles. 



Before definite conclusions can be drawn regarding any relation 

 which may be thought to exist between the clinical and experi- 

 mental conditions it will be necessary to determine whether this 

 is the only lesion which can give rise to a permanent reversal of 

 the cardiac mechanism. 



31 (727) 



The intercalated discs of atrophied heart muscle. 

 By H. E. Jordan. 



[From the Anatomical Laboratory, University of Virginia.] 



In two earlier papers 1 I presented evidence in support of my 

 interpretation of intercalated discs as irreversible contraction 

 bands. In a more recent paper the idea was tested by appearances 

 in a natural experiment, namely, extremely hypertrophied heart 

 muscle. 2 The conditions here obtaining were in perfect accord 

 with, and confirmed the plausibility of, my previous interpreta- 

 tion. Since then I have had opportunity to study lesser degrees 

 of hypertrophy, as well as an excellent specimen of atrophy 3 

 (weight of heart 180 grams). It is the purpose of this note to 

 complete my report of observations on intercalated discs by a 

 record of my findings in atrophied heart muscle, and to reempha- 

 size the point that all the evidence, including ontogenetic, com- 



1 Jordan, H. E., (1911) "The Structure of Heart Muscle of the Humming Bird, 

 with Special Reference to the Intercalated Discs," Anat. Rec, 5: 11; (1912; with 

 Mr. K. B. Steele) "A Comparative Microscopic Study of the Intercalated Discs of 

 Vertebrate Heart Muscle," Am. Journ. Anat., 13: 2. 



2 Jordan, H. E. (1912), "The Intercalated Discs of Hypertrophied Heart 

 Muscle," Anal. Rec, 6: 9. 



3 For this material I am indebted to Dr. W. H. F. Addison, of the University of 

 Pennsylvania. 



