440 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



pressure." Any tissue the meshes of which are thus engorged with lymph is 

 said to be " cedematous." l 



PART II. THE INNERVATION OF THE HEART. 



It has long been known that the frog's heart can be kept beating for many 

 hours after its removal from the body. In 1881, Martin 2 succeeded in main- 

 taining the beat of the dog's heart after its complete isolation from the central 

 nervous system and the systemic blood-vessels. Ludwig and his pupils 3 have 

 attained the same result in a different way. In 1895, Langendorff 4 was able 

 by circulating warmed oxygenated, defibrinated blood through the coronary 

 vessels to maintain the hearts of rabbits, cats, and dogs in activity after their 

 total extirpation from the body. It is evident, therefore, that the cause of the 

 rhythmic beat of the heart lies within the heart itself, and not within the cen- 

 tral nervous system. 



Cause of Rhythmic Beat. It has been much disputed whether the car- 

 diac muscle possesses the power of rhythmical contraction or whether the 

 rhythmic beat is due to the periodic stimulation of the muscle by the discharge 

 of nerve-impulses from the ganglion-cells of the heart. The arrangement of 

 the ganglion-cells and nerves suggests the latter view. 



The Intracardiac Ganglion-cells and Nerves. In the frog the cardiac nerves, 

 arise by a single branch from each vagus trunk and run along the great veins 

 through the wall of the sinus venosus, where many ganglion-cells are found, 5 

 to the auricular septum. Here they unite in a strong plexus richly provided 

 with ganglion-cells. 6 Two nerves of unequal length and thickness leave this 

 plexus and pass along the borders of the septum to the auriculo-ventricular 

 junction, where each enters a conspicuous mass of cells known as Bidder's 

 ganglion. 7 Ventricular nerves spring from these ganglia and can be followed 

 with the unaided eye some distance on the ventricle. With the chloride-of- 

 gold method, the methylene-blue stain, and especially the nitrate-of-silver im- 

 pregnation, the ventricular nerves can be traced to their termination. Some 

 difference of opinion exists regarding the manner of their distribution and the 

 precise nature of their terminal organs. The following facts, however, may be 

 considered established both for the batrachian and the mammalian heart. 8 



The ventricular nerves form a rich plexus beneath the pericardium and 

 endocardium. Branches from these plexuses form a third plexus in the myo- 

 cardium or heart muscle, from which arise a vast number of non-medullated 



1 From oZ<%ia, a swelling. 2 Martin, 1881, p. 119. 



3 Stolnikow, 1886, p. 2 ; Pawlow, 1887, p. 452. 



4 Langendorff, 1895, p. 293 ; also Martin and Applegarth, 1890, p. 275 ; Arnaud, 1891, p. 

 396 ; Heilon and Gilis, 1892, p. 760; Porter, 1896, p. 39. 5 Kemak, 1844, p. 463. 



6 Ludwig, 1848, p. 140. 7 Bidder, 1852, p. 169. 



8 The literature of this subject has been collected by Jacques (1894, p. 622; and 1896, 

 p. 517) and by Heymans and Demoor (1895, p. 619). For the development of the cardiac 

 nervous system in different classes of vertebrates, see His, Jr., 1891, pp. 1-64 ; compare His 

 and Romberg, 1890, pp. 374 and 416. 



