THE PHENOMENA NOTED DURING EACH CARDIAC CYCLE 281 



a number of phenomena which may be conveniently dealt with under 

 the following headings : (a) the changes in its form, (h) the generation 

 of electrical energy, (c) the production of sounds, {d) the variations 

 in pressure within its chambers, and (e) the changes in the position of 

 its valves. 



A. THE CHANGES IN THE FORM OF THE HEART 



Methods of Registration. — The procedures most frequently em- 

 ployed for determining the changes which the heart undergoes during 

 its systoUc and diastolic phases, may be arranged in the following 

 manner : 



(a) Observation with the help of linear measuring instruments. (Ludwig, 

 1843.) 



(6) Graphic registration by means of ordinary writing levers which are placed 

 horizontally upon different parts of the heart (von Frey), or with the help of 

 suspended levers which are connected with the cardiac musculature by strings. 

 (Gaskell, 1882, and Engelmann, 1892.) 



(c) Photographic, cinematographic, and radiographic registration. Ortho- 

 diagraph. (Zuntz and Schumberg, 1896, Buchard, 1898, and Braun, 1898.) 



(d) Acupuncture, the insertion of long needles into different regions of the 

 heart while the chest remains closed. (Jung, 1836, and Haycroft, 1890.) 



Nearly all investigations of this kind have been made either upon 

 the excised heart or upon the heart while freely exposed to the view 



Fig. 138. — Diagram to Show How the Beating Frog's Heart Adapts Itself to the 

 Surface Upon Which It Rests. The Dotted Line Indicates Diastole. 



by removing the ventral wall of the thorax. Quite obviously, either 

 one of these procedures cannot be regarded as perfect, because it 

 places this organ under abnormal conditions and tends, therefore, 

 to disturb its normal activity. At the present time, however, this diffi- 

 culty cannot be avoided and hence, it becomes necessary to correct 

 any errors from this source by indirect evidence. Inasmuch as the 

 consistency of the cardiac substance is soft during diastole and firm 

 during systole, the organ as a whole must necessarily adapt itself to 

 its surroundings and undergo certain changes in its form which, so to 

 speak, are forced upon it. Even the normal heart in situ is not fully 

 protected against the different degrees of traction which are brought 

 to bear upon it whenever the body as a whole is made to assume an 

 unusual position. 



In endeavoring to obtain a composite picture of the changes in the 

 form of the beating heart, attention should first be called to the altera- 



