214 FRANKLIN P. MALL 



been embalmed with carbolic acid, there was little opportunity 

 to use other methods with the human heart. However, car- 

 bolic acid specimens may be further prepared nearly as well as 

 fresh hearts by boiling and such secondary treatment was also 

 employed. Either boiled or fresh hearts that are to be dissected 

 subsequently or preserved permanently may be kept perfectly 

 well in a 3 per cent solution of carbolic acid or in formalin. 



Before discussing the architecture of the heart musculature it 

 is necessary to define a fiber. It is now well-known that heart 

 muscle cells form a syncytium in which may be found the primi- 

 tive fibrils of the cells. The bundles in general are parallel in 

 direction with numerous lateral branches which pass out of a 

 single group of cells at very acute angles. On account of the 

 numerous large clefts between the cells, to make room for blood 

 vessels as well as strands of connective tissue, groups of cells 

 can be separated into larger bundles or fasciculi which are clear- 

 ly recognizable to the naked eye. These are the so-called fiber 

 bundles which are not entirely free but anastomose constantly with 

 adjacent fiber bundles. It thus happens that no bundles are single 

 but they are a portion of a conthmous network which is a repe- 

 tition on a larger scale of the primitive fibrils seen under the mi- 

 croscope. The fasciculi have a general parallel direction which, 

 however, are constantly shifting in direction as they penetrate 

 the heart wall, so that ultimately the fibers on the outside of the 

 heart lie at right angles to those under the endocardium. 



The direction of the fibers is also of physiological significance ; 

 the fibers always shorten and widen in contracting, so that a 

 square centhneter of surface becomes shorter and not wider in 

 the direction of its fibers, but thicker in the direction of the 

 thickness of the heart wall. In the change of shape from dias- 

 tole to systole the external surface of the heart becomes smaller 

 and the thickness of wall becomes greater. This is all well known. 



In stripping off the fibres it is found that successive bundles 

 are constantly passing under one another so that they overlap 

 much as do the shingles of a roof. The outer fibers which arise 

 at the base send small bands into the depth which have a tend- 

 ency to turn upon themselves to return to the base. This is 



