INTERCALATED DISCS OF HEART MUSCLE 173 



6. The discs are interpreted in terms of local contractions (or 

 aggregations of 'anisotropic' granules) in the muscle fibrils. The 

 different modes of association of such single contraction foci 

 give rise to all the various types of discs described, i.e., granules, 

 blocks, ovals, plates (composed of closely apposed longer and 

 shorter rodlets), 'combs,' 'steps' and saw-teeth forms. 

 . 7. The presence of discs would seem to be correlated with the 

 function of rhythmic contraction characteristic of cardiac muscle, 

 and may represent a fixed phase of a contraction wave (local or 

 general), or more probably is the result (of the nature of an irre- 

 versible strain condition) of the total amount of function. The 

 latter idea is supported by the fact of (a) their absence in the 

 mammalian foetus, and their increasing abundance and coarse- 

 ness with age; (b) their general location in lines corresponding 

 roughly with the axes of the heart muscle mesh; (c) in general, 

 their greater abundance in hearts of more rapid beat; and (d) 

 their presence also in the striated muscle of the -media in the proxi- 

 mal (beating) end of the pulmonary arteries (e.g., mouse). 



LITERATURE CITED 



Heidenhain, M. 1901 Uber die Struktur des menschlichen Herzmuskels- 

 Anat. Ariz., Bd. 20. 



1911 Plasma und Zelle. Jena. 



Jordan*, H. E. 1911 The structure of heart muscle of the humming bird, with 

 special reference to the intercalated discs. Anat. Rec, vol. 5, no. 11. 



Marceau, F. 1904 Recherches sur la structure et le developpement compare 

 des fibres cardiaque. Ann. des Sc. Nat. Zool., vol. 19. 



Palczewska, Irene von* 1910 Uber die Struktur der menschlichen Herzmuskel- 

 fasern. Arch. f. mikr. Anat. u. Entwickl., Bd. 75. 



Werner, Marie 1910 Besteht die Herzmuskulatur der Saugetiere aus allseits 

 scharf begrenzten Zellen oder nicht? Arch, f . mikr. Anat. u. Entwickl., 

 Bd. 75. 



Zimmermann, K. W. 1910 Uber den Ban der Herzmuskulatur. Arch. f. mikr. 

 Anat. u. Entwickl., Bd. 75. 



