190 AN AMERICA* TEXT-BOOK OF PHYSIOLOGY. 



of the contraction, however, is altered by the calcium, the relaxation of the 

 ventricle being sometimes so much delayed that the next contraction takes 

 place before the relaxation from the previous contraction has commenced, the 

 ventricle falling- thereby into a state of persistent or " tonic" contraction. The 

 additiou of a potassium sail restores the normal character of the contraction, 

 calcium and potassium having an antagonistic action on the heart. 1 The 

 importance of calcium to the heart is said to be demonstrated by the disap- 

 pearance of the spontaneous contractions of the heart which follows the pre- 

 cipitation of the calcium in the circulating fluid by the addition to it of an 

 equivalent quantity of a soluble oxalate, and by the return of spontaneous 

 contractions which is seen when the calcium is restored to the solution. 



The antagonistic action of calcium and the oxalates was first pointed out 

 by (yon. 



According; to Ringer, the substances thus far mentioned are effective in the 

 following order : normal saline is the least effective; next is saline containing 

 sodium bicarbonate; then saline containing tricalcium phosphate; and best of 

 all, saline containing tricalcium phosphate together with potassium chloride. 

 He recommends the following mixture: Sodium chloride solution ().(> per 

 cent., saturated with tribasic calcium phosphate, 100 cubic centimeters; solu- 

 tion potassium chloride 1 per cent., or acid potassium phosphate (HK 2 POJ 

 1 per cent., 2 cubic centimeters. 2 



There has been considerable dispute over the part played by oxygen in 

 the beat of the frog's heart. McGuire and Klug were of opinion that 

 the beat is largely independent of the amount of oxygen in the circulating 

 fluid. Yeo concluded that the contracting heart uses more oxygen than 

 the resting heart, and that the consumption of oxygen increases with the work 

 done. Kronecker and Handler, on the contrary, believe that the oxygen con- 

 sumption is increased by an increase in the rate of beat, but is independent of 

 the work done. More recent observers are united on the necessity of oxygen 

 to the working heart. Oehrwall's studies in this field are especially interesting. 

 He finds that a volume of blood sufficient to fill the frog's ventricle will main- 

 tain contractions for hours provided the heart is surrounded by an atmosphere of 

 oxygen. The heart is brought to a stand by lack of oxygen and may be made 

 to beat again, even after an arrest of twenty minutes, by giving it a fresh sup- 

 ply. The heart fails in oxygen-hunger probably because the chemical process 

 by which the stimulus to contraction is called forth no longer takes place, and 

 not because of a failure in contractility, for even after long inaction a gentle 

 touch on the pericardium will cause a vigorous contraction.' 5 



Haldane 4 discovered that the corpuscles of the blood are not essential to 

 the contractions of the warm-blooded heart, provided the oxygen which the 



'Bottazzi: Archives de Physiologic, L896, xxviii. p. 882. 

 Ringer : Journal of Phusiolixjij, 1893, xiv. p. 128. The bibliography has recently been given 

 by Unwell: American Journal of Physiology, 1898, ii. p. 47 ; and Greene : Ibid., p.82; consult 

 also White : Journal of Physiology, 1896, xix. p. 344. 



Oehrwall: Skandinavisches Archivfur Physiologic, 1898, viii. p. 1. 

 * Haldane: Journal of Physiology, 1895, xviii. p. 211. 



