314 H. E. JORDAN AND J. B. BANKS 



IV. DISCUSSION 



It becomes a relatively easy matter to support, on the basis 

 of observational data, any one of the earlier-proposed hypoth- 

 eses regarding the significance of the intercalated discs if only 

 discs of a certain tj^pe are selected as representing the original 

 form, and others regarded as secondary modifications. For ex- 

 ample, certain regions may be found in abundance in which nu- 

 cleated areas of coarse trabeculae and related branches are clearly 

 and sharply demarked from similar areas by a fairly uniform type 

 of band- and terraced-discs. Such have been published almost 

 exclusively in support of the intercellular nature of the discs 

 by Palczewska (20) and by Werner (23). No interpretation is 

 attempted by these investigators of such discs as are illustrated 

 in figures 22, 23 and 24. If we combine with such evidence also 

 the results of macerating cardiac muscle, when areas similar to 

 those above-described for sections are isolated; and the further 

 fact that silver nitrate is precipitated by the intercalated discs, 

 the evidence at first seems complete that the myocardium is 

 compounded of distinct cells. But such interpretation must ig- 

 nore the facts that cardiac muscle is originally syncytial, that 

 discs appear only gradually during fetal (from about the second 

 month) and infantile life, and that the nucleated areas outlined 

 by the discs and sarcolemma do not correspond closely with the 

 original stellate myoblasts of the embryonic myocardium nor 

 with their later fusiform and cylindric modifications. If we add 

 to these countervailing facts the further facts that many discs 

 are of very irregular character (e.g., figs. 24 to 27) and that 

 they are only incomplete peripheral band-like structures (not 

 membranes passing from surface to surface) occasionally super- 

 nuclear in position, an intercellular interpretation becomes 

 untenable. 



Discs like the one illustrated in figure 21 seem to support 

 Heidenhain's opinion that they represent areas from which new 

 sarcomeres arise. But the great majority of the discs are very 

 different from such a structure, and cannot be interpreted in this 

 manner. Nor do such discs resemble the differentiating sar- 



