AN ANATOMICAL STUDY ON THE 



From these facts it seems clear to me that the 

 motion of the heart consists of a tightening all over, 

 both contraction along the fibers, and constriction 

 everywhere. In its movement it becomes erect, 

 hard, and smaller. The motion is just the same as 

 that of muscles when contracting along their ten- 

 dons and fibers. The muscles in action become tense 

 and tough, and lose their softness in becoming hard, 

 while they thicken and stand out.^ The heart acts 

 similarly. 



From these points it is reasonable to conclude that 

 the heart at the moment it acts, becomes constricted 

 all over, thicker in its walls and smaller in its ven- 

 tricles, in order to expel its content of blood. This 

 is clear from the fourth observation above in which 

 it was noted that the heart becomes pale when it 

 squeezes the blood out during contraction, but 

 when quiet in relaxation the deep blood red color 

 returns as the ventricle fills again with blood. But 



^ Niels Stensen (1638-1686), the Danish anatomist who later became 

 a bishop of the Roman church, is usually credited with recognizing 

 the muscular character of the heart {De Musculis et Glandulis Observa- 

 tionum Specimen, 1664). This is a little unfair to Harvey, and, for that 

 matter, to the unknown aathor of the Hippocratic tract on the heart 

 to which Harvey refers in Chapter XVII. Stensen, as far as I can de- 

 termine, did little more than these in comparing the heart's contraction 

 to that of a muscle, and then saying that it is nothing more than muscle. 

 The structural (histological) similarity between the heart and muscle 

 was shown in A. Leeuwenhoek's (1632-1723) Arcana Naturae (Delft, 

 1695), in which Epistola 82 (page 445) gives the first clear account of 

 the peculiar structure of cardiac muscle, with excellent illustrations. 

 For an interesting account of Stensen, see Dr. W. S. Miller's paper, 

 Johns Hopkins Hosp. Bull., 25: 44 (Feb.) 1914. 



I 30] 



