284 THE MECHANICS OF THE HEART 



In accordance with the observations made upon the excised heart, 

 it may seem surprising that the changes in the different diameters of 

 the heart do not cause the apex to be displaced in an ahnost straight 

 Hne upward toward the base. Different reasons may be given for its 

 relative immobility. While it must be granted that the heart is more 

 firmly anchored at its base on account of the firm support afforded it 

 by the large blood-vessels, it must be remembered that the pericardial 

 sac, together with its mediastinal fastenings to the diaphragm, pos- 

 sesses the tendency of counteracting any distinct displacement of the 

 apex. . It is also claimed that the discharging heart suffers a recoil in 

 the manner of a cannon on being fired, ^ and secondly, that the sudden 

 distention and straightening out of the aorta and pulmonary artery 

 by the escaping ventricular blood causes the basal region to recede 

 somewhat in a downward direction. The ventricle being thus opposed 

 by a resistance above, must remain in its former position. ^ 



Fig. 142. — Cardiograph. 

 This is strapped around the chest, the central button is applied to the "apex-beat" 

 and its pressure on the chest wall regulated by means of the three screws at the sides. 

 The tube at the upper part of the instrument serves to connect the drum of the cardio- 

 graph with a registering tambour, such as is shown in Fig. 143. (Sanderson.) 



The Cardiogram. — A graphic record of the cardiac impulse or 

 apex beat may be obtained with the help of two Marey tambours, 

 one of which is fastened to the surface of the chest (Fig. 142) in the area 

 previously designated, and the other upon a stand in relation with the 

 smoked paper of a kymograph (Fig. 143). When connected by means 

 of rubber tubing, the membranes of these tambours must oscillate in 

 unison. If the membrane upon the receiving tambour is pressed in- 

 ward by the bulging chest wall, the writing lever attached to the re- 

 cording drum must move upward, and vice versa. 



This instrument is known as the cardiograph, and the record made 

 by it as the cardiogram. Not much importance can be attached to it 



^ Skoda, Abh. iiber Perc. und Auskultation, Wien, 1847, also see : Feuerbach, 

 Pfliiger's Archiv, xiv, 1877. 



^ Sena, Traite de la struct, du coeur., Paris, 1849, or Aufrecht, Deutsch. Arch, 

 fiir klin. Med., Nr. 19, 1877. 



