613 



"Segmentation"' of the heart muscle is usually defined as a rupture 

 of the muscle occurring in the "cement-substance" between the "heart 

 muscle cells''. There may be, also, incomplete rupture along the line 

 of the "cement substance". Pathologically, the condition is thought 

 to be caused by some agent which brings about a softening or a 

 solution of this "cement", thus allowing the "cells" to be pulled 

 apart by the contraction of unaffected parts of the musculature. 

 ScHLATER, in one of the most recent contributions we have been able 

 to find on this subject, stated a somewhat different view. He believes 

 that "segmentation" may occur along what he calls "intercalated 

 discs''. But he bases his study upon the work of Marceau, and his 

 interpretation of the condition of "segmentation" is for all purposes 

 the same as that of other writers who speak of separation along 

 "cement-lines". Marceau considers the intercalated discs to be inter- 

 cellular structures of tendon-like character, to which the muscle 

 fibrillae are attached and against which they pull in contraction; the 

 basal assumption of Marceau being that heart muscle is cellular. 



"Fragmentation" is regarded as being due to ruptures in the 

 "cell-bodies" and does not involve the "cement-lines". (The reader 

 is referred to the articles cited at the end of this paper; fi'om them, 

 and particularly from those of Hektoen and MacCallum, full historical 

 information can be gotten.) 



Various elaborations of these definitions are advanced by the 

 writers referred to, but the fundamental assumption is the same; 

 namely, that the heart muscle is cellular in structure. 



It is the intention of this paper to present evidence to show 

 that the accepted classification of ruptures of the heart muscle as 

 "segmentations'' and "fragmentations" (depending respectively upon 

 the location of such ruptures outside of or within the so-called "heart 

 muscle cells") is incorrect, and that the interpretations of the patho- 

 logy of these conditions must therefore be revised. 



In the two papers recently presented by Jordan, the second of 

 which was prepared with the assistance of Steele, there are reported 

 extensive studies of the histology of cardiac muscle in numerous 

 animals, with especial reference to the intercalated discs. These 

 intercalated discs are the same structures as the "cement-lines" spoken 

 of by Hektoen, MacCallum and others. After describing the general 

 appearance and location of these lines, Hektoen states that "the lines 

 may be straight or curved, as is usually the case, or crooked, zigzag, 



