294 TEXT-BOOK OF PHYSIOLOGY 



A, expresses auricular activity, J l and F express respectively the initial and 

 final activity of the ventricle. The letters Ap indicate a negative wave 

 following auricular activity; h, represents the time during which the excita- 

 tion process is passing through the auriculo-ventricular bundle (bundle of 

 His) from its origin to its terminations. J designates a wave which initiates 

 the ventricular contraction and is the result of the contraction of the system 

 of papillary muscles. It is preceded and followed by negative waves Ja 

 and Jp. The horizontal portion of the record, t, represents the contraction 

 of the middle layers of the muscle fibers of the ventricle. F represents the 

 contraction of the muscle fibers in the region of the conus arteriosus; and is 

 likewise preceded and followed by negative waves Fa, and Fp. P represents 

 the pause in the heart activities. 



The activities of the different parts of the heart indicated by the lettering 

 may be summarized as follows: (Ott.) 



Phase of Electrocardiogram. Approximately. 



A. Activity of i presystole. Period of filling of the heart (ventricle). 



/. " " papillary system intersystole. Period of distention of the heart. 

 t. u middle layer of ] 



ventricular muscle \ systole. Period of ventricular discharge. 

 F. " " conus arteriosus J 

 P. Rest of the whole heart pause of heart. Period of filling of the heart. 



In pathologic conditions of the heart muscle there are many deviations 

 from the normal electrocardiogram which are more or less characteristic 

 and of diagnostic value and importance. 



THE BLOOD-SUPPLY TO THE HEART 



The nutrition of the heart, its irritability and contractility, the force 

 and frequency of the beat, are dependent on and maintained by the intro- 

 duction of arterialized blood into and the removal of waste products from 

 its tissue. 



In frogs and allied animals the heart muscle is nourished by the blood 

 flowing through its cavities. During the diastole the blood, under the 

 influence of the slight pressure developed, passes from the interior 

 of the heart into a system of irregular passage-ways or channels, which 

 penetrate the heart-wall in all directions and thus comes into direct contact 

 with the heart-cells. With the beginning of the systole the blood is forced 

 out of these channels into the interior of the ventricle, bringing with it the 

 products of tissue metabolism. 



In mammals the entire inner surface of the heart, as shown by 

 the investigations of Pratt, also presents a series of openings, the foramina 

 of Thebesius, which lead into a similar series of passage-ways penetrating 

 in various directions the heart-walls, and there are reasons for believing 

 that the heart of the mammal may be to some extent nourished in a manner 

 similar to the manner by which the frog heart is nourished. Thus, if a 

 glass tube be inserted and fastened into the aortic opening of the excised 

 heart of a cat and the interior of the ventricle filled with warm defibrinated 

 blood of the same animal, under a pressure of about 75 mm., the heart will 

 recommence and continue to beat for a period varying from one to several 



1 / has the significance here of /. 



