vii MECHANICS OF THE HEAKT 209 



nients are retarded, the diastolic aspiration increases so much that 

 the tube connected with the ventricle is emptied. 



(d) If the hollow of the pericardial chamber is iilled with milk, 

 and connected with a horizontal glass tube, containing a fluid to 

 serve as index, the total volume of the heart will be found to 

 increase during diastole, while with gentle stimulation of the 

 vagus this diastolic increase of volume is still further augmented. 

 This phenomenon is not necessarily connected with slowing of the 

 heart's action, since the same thing can be seen in the frog with 

 no appreciable changes in systolic frequency. (Coats.) 



The conclusions we deduced from this and other facts had the 

 rare fortune of being confirmed by more complete and decisive 

 experiments. A. Fick (1873) showed by means of the metal 

 manometer, which he connected up with the right or left ventricle 

 of the dog (by a sound introduced through the jugular vein or 

 carotid), that pressure sinks below the zero line during diastole. 

 Goltz and Gaule (1878) endeavoured with their minimum mano- 

 meter to determine the absolute value of the negative diastolic 

 pressure with open thorax, and found that it may amount to 

 - 320 mm. of water in the left, and - 25 mm. in the right ventricle, 

 and diminishes progressively with the weakening of systole, i.e. in 

 proportion as the" systolic evacuation becomes less complete. The 

 values obtained by De Jager by the same methods were higher : 

 he found a negative pressure that may amount to - 38 mm. Hg. 

 in the left, and - 6 mm. Hg. in the right ventricle. Values 

 approximating very closely to these were obtained by other 

 workers, e.g. Eolleston, v. Frey, and Krehl (1890), with the elastic 

 manometer, both with closed and with open thorax. 



It was Stefani, however, who directly undertook the task of , 

 experimentally checking, one by one, the propositions which 

 we had formulated in 1871, and repeated with certain altera- , 

 tions in 1874 and 1876. In a series of interesting memoirs (1877- 

 1891) he placed on a firm experimental basis that same doctrine 

 of the activity of cardiac diastole which we had preached for 

 many years with ever-growing conviction, adding many new 

 arguments in its favour. 



It is essential to the comprehension of this theory to premise that 

 the thesis of active diastole may be considered from two different 

 points of view. The diastole may be considered active in a purely 

 mechanical sense, viz. that the refilling of the ventricles during 

 the first period of perisystole is the effect not of the vis a tergo of 

 the blood descending from the auricles into the ventricles, but of 

 the aspiration developed by the latter during that interval. The 

 expression active can, however, also be employed in a strict 

 physiological sense, viz. that the diastole is controlled and regulated 

 the action of the vagus. Let us first consider the mechanical 

 aspect. 



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