ACTION OF THE HEART. 307 



observed iu these sections has been proposed by Eckhard and Bidder, and by 

 Dr. Michael Foster. Eckhard and Bidder, observing that the movements 

 called forth by the last-mentioned division soon cease, attribute them not to 

 the action of spontaneously acting ganglia, but merely to irritation of the 

 accelerating fibres and ganglia, and this is supported by the fact that Stan- 

 nius's experiment will succeed when the inhibitory centres are paralyzed by 

 atropine. Dr. Foster 1 again believes that the iutracardiac ganglia of the 

 heart exert a continuous influence, and that the rhythmical action is due to a 

 peculiarity of the muscular tissue. The cardio-motor system of nerves rep- 

 resented in the figure on p. 310, which is purely diagrammatic, by a single 

 stellate ganglion, receiving and giving off afferent or excitor and efferent or 

 motor nerves, may be excited by mechanical, chemical, electric, and thermic 

 stimuli. Bernard, for example, observed acceleration of the heart's beats 

 when the bulb of a thermometer, introduced through the superior vena cava, 

 touched the endocardium ; and a similar effect was noticed (in Mammals at 

 least, though the opposite occurred in cold-blooded animals) by Ludwig when 

 the blood-pressure was increased. Again, the presence of blood or serum in 

 the chambers of the heart greatly prolongs its activity, partly by its mechanical 

 excitation, but partly also by affording nutritive materials and a supply of 

 oxygen. The heart may be temporarily arrested, even during life, by a strong 

 expiration, which appears to act by effecting the compression of its walls, 

 and preventing the entrance of fresh blood, though perhaps other causes here 

 co-operate. The importance of oxygen is well shown by an experiment made 

 by Wu'ndt, 2 who observed that the heart of a frog continued to beat for twelve 

 hours in oxygen, whilst it ceased to move in ordinary air after three hours, 

 in nitrogen and hydrogen after one hour, and in vacuo in half an hour. 

 Certain gases, as chlorine, sulphurous acid, hydrogen sulphide, and certain 

 poisons, as strychnia, opium, Calabar bean. 3 are capable of more or less 

 rapidly arresting the movements of the excised heart when directly applied 

 to it, by their chemical action on the cardio-motor system. Various salts, 

 as those of sodium and rubidium (Grandeau and Bernard) when in large 

 quantity, and those of the biliary acids (Rohrig) slow or arrest the heart's 

 action ; as do also certain acids, as acetic and citric acid (Bobrik), and phos- 

 phoric acid (Leyden and Muuk). The action of electricity upon the heart 

 is peculiar. The heart, as Eckhard has remarked, knows no tetanus. A 

 single shock applied to it in situ increases the frequency of its beats, and if 

 applied to the excited heart when its excitability is nearly exhausted, stimu- 

 lates it to renewed rhythmical activity; but interrupted currents, which if 

 applied to ordinary muscles would produce tetanus, abolish the rhythmical 

 activity of the centres now under consideration, and ineffective peristaltic con- 

 tractions occur, with great depression of the blood-pressure. 4 Continuous cur- 

 rents have the same effect. 



243. Effects of Variations of Temperature upon the Heart's Action. The 

 effects of variations of temperature upon the heart have been studied by 

 Pickford, 5 Calliburces, 6 Tigger, 7 Liebermeister, 8 Schelske, 9 Panum, 10 Cyon, 11 

 and Bruntou. 12 From their experiments, which were chiefly made on the 



1 Journ. of Anat. and Physiol., 1869, p. 400. 2 Physiologic, 1873, p. 319. 



3 See Fraser, Trans. Roy/Soc. Edinb , vol. xxiv, p. 65. 



4 Mayer, quoted in Hermann's Physiologic, 1874, p. 75. 



5 Henle and Pfeuff, Zeits., 1851. ' 6 Gaz. Hebdomad., 1857, p. 468. 



7 Dissert., 1853. 8 Deutsch. Arcliiv. f. Klin. Med., Bd. i, p. 464. 



9 Ueber der Veranderungen der Erregbarkeit durch die Warme, Heidelberg, 1800. 



10 See Abstract in Schmidt's Jahrbucher, 1858. 



11 Ludwig's Arbeiten, 1868, p. 77. 



12 St. Bartholomew's Hosp. Pveports, vol. vii, 1871, p. 216. 



