INTERCALATED DISCS OF THE HEART OF BEEF 287 



of discs can not be ranged into a consecutive series leading to a 

 completely differentiated sarcomere. 



Marceau's interpretation is at first consideration more plau- 

 sible, especially in view of the facts that the discs very generally 

 divide areas of different physiologic states, and that, at least in 

 certain arthropod muscles, e.g., leg muscle of sea-spider and scor- 

 pion (Jordan (10 and 12) ), the tendon fibrils apparently dif- 

 ferentiate from original myofibrils; but it meets with the objec- 

 tion that the discs do not react to specific stains for tendinous 

 tissue, e.g., van Gieson's stain (and the Bielschowsky technic; 

 Dietrich), and that the discs frequently lie within either con- 

 tracted or relaxed areas. 



Dietrich's interpretation of the discs as coordination mechan- 

 isms is no more than a suggestion, and no direct evidence is given 

 in its support. 



The original interpretation of the discs as intercellular cement- 

 substance finds good support only in the fact that macerated 

 myocardium dissociates into elements bounded by discs and sar- 

 colemma. But these elements do not closely resemble the stel- 

 late and fusiform cell-areas of the original embryonic myocardial 

 syncytium, nor the fusiform elements of the early fetal myocar- 

 dium. Furthermore, the earlier fetal heart is composed of an- 

 astomosing, branched, cylindric trabeculae, forming a continu- 

 ous network, apparently without sign of typical discs. After 

 prolonged maceration the heart muscle fragments also along the 

 telophi'agmata. The intercalated discs are always associated 

 in some manner with the telophragmata, hence in fragmenting 

 myocardium the plane of fracture must necessarily frequently 

 involve a disc. When we add to these facts the probability 

 that the discs as modified portions of the myofibrils are lines 

 of relative weakness, the behavior of the rnacerating myo- 

 cardium becomes readily comprehensible. 



The conduct of the discs towards silver nitrate solutions also 

 need not necessarily indicate an essential intercellular cement- 

 substance as a constituent of the discs. It may mean only that 

 the discs are regions of relatively greater abundance of the more 

 fluid portion of the interfibrillar sarcoplasm, which may precipi- 



