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



Iroiii the standpoint of disc-fovniation fusions, however, are 

 of two sorts: (1) such as furnish the causal factor; and (2) such 

 as simply distort, displace, or modify in some way, discs already 

 present in the fibers involved in the fusion. The second sort is 

 illustrated semidiagrammatically in figure 11. Here two fibers 

 have become fused in such a manner as to produce an an har- 

 monic alinement of telophragmata in the apposed fibers, the result 

 of the superposition of a mutual spiral twisting around a common 

 axis of the tw^o fibers. Such spiral twistings and fusions are 

 common. They have been described also in scorpion voluntary 

 striped muscle (Jordan (12) ) and in human heart muscle 

 (Heidenhain (4) ). According to Heidenhain a similar condi- 

 tion results from the spiral twisting of a single fiber about its 

 central axis (''Plasma und Zelle," p. 616). The festooned sarco- 

 lemma, according to Heidenhain's interpretation, would here 

 represent inturned portions of the originally peripheral mem- 

 brane. The same condition would result, how^ever, if tw^o adja- 

 cent fibers fused in such a manner that the crest of a festoon 

 of one side alternated with the trough between tW'O successive 

 festoons on the apposed fiber. The latter method appears to 

 be more common, though the former probably also occurs. At 

 any rate the spiral twisting of the myocardial trabeculae during 

 development and grow^th is a characteristic of the mammalian 

 heart (e.g., bulbo-spiral bundle of fibers). Under these condi- 

 tions the definitive position and relationships of the original 

 discs is secondary, a modification resulting from the twisting 

 and fusion of the fibers. 



In figure 12 is illustrated a rare type of disc. Two fibers seem 

 to have fused in an oblique plane, end to end. The terraced 

 disc is explicable on the basis of our hj-pothesis of strain effects 

 following unusual stresses, and resulting in irreversible contrac- 

 tion bands. The form of this particular disc may also be in 

 part the result of a spiral twisting of the fiber. 



In figure 13 a long terraced disc separates a deeper-staining 

 (contracted) region sharply from a lighter-staining region. One 

 of the intervals here, as frequently in such discs, between suc- 

 cessive terraces is of the length of two sarcomeres. On raising 



