616 



la au excellent specimen of atrophied heart of ISO grammes 

 (kindly supplied by Dr. W. H. F. Addison of the University of Penn- 

 sylvania) the discs, on the contrary, are all of the "comb-type". 

 Fragmentation occurs always through the lines of the discs. (Figs. 

 5 to 7 illustrate the various types of discs occurring in hypertrophied 

 fibres. Fig. 7 illustrates the exclusive type in extreme hypertrophy, 

 the preponderating type in lesser hypertrophies.) 



All the evidence from a microscopic study of pathological heart 

 tissue indicates cogently that the discs are the structures primarily 

 involved in rupture of the muscle fibres. Since the discs can not be 

 interpreted as cell boundaries, as was shown above, and as ruptures, 

 wherever they occur, always take place in the discs, the anatomical 





Fig. 4. Fig. 5. Fig. 6. Fig. 7. 



Fig. 4. Diagram of a common condition in mammalian and avian heart fibres. 

 A variable number of discs may be associated to produce step forms. 



Fig. 5. A fairly common type of disc in normal mammalian heart muscle fibres; 

 derived from the simpler type by elongation of the structural units (rodlets). 



Fig. 6. Rare type of disc in normal mammalian heart fibre; derived from types 

 4 and 6 by process of a combination of tensions in the longitudinal and transverse 

 axis, combined with longitudinal splitting of fibrils. 



Fig. 7. Exclusive type of disc in hypertrophied heart muscle fibre; derived 

 from that of Fig. 6 by exaggeration of the same process. 



distinction between "segmentation" and "fragmentation" disappears. 

 The two processes are essentially the same anatomically. Because of 

 the fact that the ruptures are more uniform and less comminuting in 

 "segmentation" than in "fragmentation", we are inclined to believe 

 that "fragmentation" may be simply a more extensive and severe 

 manifestation of the same process which occurs, in lesser degree, in 

 ''segmentation". Whatever be the nature of the pathological process 

 or processes involved in the production of the condition, however, 

 upon anatomical grounds the use of the two terms, "segmentation" 

 and "fragmentation" is not justifiable. 



