VII 



MECHANICS OF THE HEAET 



185 



in diastole, it is necessary to prepare it with the acid under a pressure of 

 60 mm. mercury. This may be a complete success, but often fails, owing to 

 the easy rupture of the heart, more particularly of the auricles. After 

 submitting it to the action of the acid for about three hours, the heart is laid 

 for several days in water, in which the connective tissue, softened by the 

 acid, partly dissolves, and the rest can be readily separated from the muscular 

 tissue. The muscle fibres can then be teased out without difficulty. 



B 



B' 



FIG. 55. A, Section through heart of a criminal, fixed in systole, at limit of lower third of ventricles. 

 A', Section through same heart, at limit of upper third. B, Section through heart of approxi- 

 mately the same size as the preceding, fixed in diastole, at same level as A. B', Section of 

 same heart, at level of A'. All four figures are diminished by half. (Krehl.) 



The cavity of the left ventricle, seen in section, appears in 

 systole as an irregular, somewhat star-shaped fissure, the centre of 

 which corresponds with the conus arteriosus. This proves that 

 the left -ventricle is unable to empty itself completely, even in 

 maximal contraction, so that a small quantity of blood is left in 

 it, more especially in the space immediately behind the semilunar 

 valves of the aorta. Its driving power depends mainly on the 

 middle layer, contraction of which must produce a lengthening 

 of the longitudinal diameter of the ventricle : this is, however, 



