INTERCALATED DISCS OF THE HEART OF BEEF 291 



In figure 2 a terraced or step-form of disc is shown in connec- 

 tion with simpler discs of the character above described. That 

 the latter type may be bisected by the telophragma is demon- 

 strated by the manner of the attachment of the sarcolemma 

 festoons. The same point is even more clearly demonstrated in 

 teased preparations. The figure illustrates also another common 

 feature in connection with the discs, namely, the division of a 

 contracted from a relaxed area along the line of the discs. In 

 the upper relaxed region are seen the telophragmata, the Q-discs 

 and the J-discs; in the lower contracted region delicate con- 

 traction bands alternate with lighter discs. The contracted 

 region stains more intensely than the non-contracted region. The 

 discs evidently frequently act as barriers to the spread of a 

 particular physiologic state; but occasionally the discs are 

 crossed by functional phases, and so may lie in either contracted 

 or relaxed areas. 



It should be noted also that in the terraced portion of this com- 

 plex disc the successive steps are so arranged that the upper border 

 of any one is in line with the lower border of the next higher disc, 

 and the left hand border of any one is in line with right hand 

 border of the next higher disc ; that is, the arrangement is such as 

 would result if the several steps had originally formed portions 

 of the same continuous band at the upper level and had been 

 divided into smaller sections, which were subsequently drawn 

 to successively lower sarcomeric levels in a lateral progression. 

 Moreover, certain terraces are united by a deeper-staining mem- 

 brane or 'riser;' and the relation of the involved telophragmata 

 is such that the membranes of opposite sides join opposite sur- 

 faces of the discs. Such discs are common (figs. 5, 9 and 13), 

 and the more general condition of terraced discs with respect to 

 the association of the steps and the included telophragmata is like 

 the one here described. But several chief variations occur: (1) 

 The terraces may ascend again foUownig a descent (fig. 27) ; (2) 

 all of the levels need not be placed in the regular order above 

 described (fig. 9); and (3) the telophragmata may be similarly 

 placed on both sides of the discs. Illustration figure 2 shows 

 further the usual location of the discs at points where the coarser 



