ix CAEDIAC MUSCLE AND NERVES 337 



centres are in continuous slight excitation, on which depends the 

 tone of the vagi, exhibited in the acceleration of* the beats, on 

 simple division of that nerve, or administration of atropin. This 

 effect does not appear when section of the vagus is preceded by 

 division of the cervical cord (Bernstein). Acceleration is also 

 obtained after dividing the splanchnic nerve (Asp), due not 

 to the lowering oT blood pressure, which usually produces the 

 opposite effect, but to the depression of vagal tonus. In the 

 newborn, tonicity seems to be wanting in the vagus till after the 

 second week, since in kittens neither section of the vagus nor 

 exhibition of atropine causes acceleration of pulse (Soltmann). 



It is possible that the systolic nerves and centres also have 

 normally a certain tonicity, although subordinate to the diastolic 

 nerves. After extirpation of the lower cervical and stellate 

 ganglia on both sides, there is, when the vagi are divided, a 

 marked acceleration of rhythm (Tschirjew, Strieker, and Wagner). 

 With intact vagi, a permanent slowing of beat can be obtained 

 on dividing the accelerators (Timofeew). 



The tone of the cardiac centres and nerves may be automatic or 

 reflex, or as is most probable, automatic and reflex in character. It 

 is known that the frequency of cardiac rhythm normally stands 

 in inverse ratio to the height of the average arterial blood pressure, 

 i.e. that rise of blood pressure produces lowering of pulse frequency 

 and vice versa. After section of the vagi this ratio is no longer 

 so distinct and constant, showing that the blood-pressure regulates 

 the tone of the cardiac nerve centres, those of the vagus in 

 particular, directly or reflexly. 



BIBLIOGRAPHY 



In addition to previous Bibliographies, see also : 



Fundamental Memoirs in re Physiology of Cardiac Muscle and Intracardiac 

 Nervous System : 



STANNIUS. Arch. f. Anat. u. Physiol., 1852. 



ECKHAKD. Beitrage zur Anat. und Physiol. Giessen, 1858-60. Experimentelle 



Physiol. des Nervensystems. Giessen, 1866. 

 GOLTZ. Arch, fur path. Anat., 1860-62. 

 BOWDITCH. Ber. d. sachs. Ges. d. Wiss., 1871. 

 LUCIANI. Ber. d. sachs. Ges. d. Wiss., 1873. Edizione italiana, Rivista clinica 



di Bologna, 1873. 



KRONF.CKER und STIRLING. Beitrage zur Anat. und Physiol., 1874. 

 MAREY. Compt. rend., 1879. 



GASKELL. Aruh. de physiol. normale et pathologique par Brown-Sequard, 1888. 

 FANO: Lo Sperimentale, 1885. Archivio per le scienze mediche, 1890. Archives 



ital. de biologic, 1888. 



ENGELMANN. Arch, neerlandaises, 1893-97. Arch. f. Anat. u. Physiol., 1902. 

 KRONECKEK. Zeitschrift fiir Biologie, 1897. 



BOTTAZZI. Pubblicazioni del R. Istituto di Studi superiori di Firenze, 1897. 

 H. E. HERING. Pfliigers Arch. Ixxxvi , 1901 ; cxv., 1906 ; cxvi., 1907. 

 A. J. CARLSON. American Journal of Physiology, xii., 1905. 

 F. B. HOFMANN. Nagel's Handbuch der Physiol. i., 1905. 

 M. HUMBLET. Arch, intern, de Physiol., 1904, i. 

 E. VON CYON. Die Nerven des Herzens. Berlin, 1907. 



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