612 
232) 
ae Sy = 
Sens 
=; 
= 
2 EHE 4} 
Fig. 1. Longitudinal section of adult human heart muscle, showing the junction of 
two cells. 
Fig. 2. Longitudinal section of heart muscle from an adult dog, showing proto- 
plasmie bridges between two cells. 
to make out this structure, its place being taken by what correspond 
to the structures, which, in other tissues, are ordinarily described as 
protoplasmic bridges. When the heart muscle of the dog and cat is 
stained by the osmic acid method, the characteristic appearance of 
bridges as pictured by KoLossow !) and GARTEN ?) can be distinctly 
made out (Fig. 2), although they have not, up to this time, been 
described in heart muscle. 
In longitudinal sections of human heart muscle tissue stained by 
KoLossow’s method, the cell is seen to consist of regular deeply 
staining masses running in the long axis of the fibre, corresponding 
with what v. KOELLIKER has described as Muskelsäulchen. These are 
separated by clear unstained spaces, the undifferentiated sarcoplasm. 
More careful observation reveals a definite relation between these 
structures. As represented in Fig. 3, the clear substance is present 
in every case on all sides of the fibril bundles, which are marked by 
the main striations present in voluntary muscle, that is, by a narrow 
disc (the Zwischenscheibe or Krause’s membrane), and a broader band 
1) A. Korossow, Ueber die Structur des Pleuroperitonäal- und Ge- 
fäßepithels (Endothels). Arch. f. mikrosk. Anat, Bd. 42, 1893, p. 318. 
2) S. Garren, Die Intercellularbrücken der Epithelien und ihre 
Function. Arch. f. Anat. u. Physiol., Physiol. Abt., 1895, p. 407. 
