220 



PHYSIOLOGY 



CHAP. 



and the venous pressure to 12-18 cm. H 2 0. If one vagus is 

 stimulated by an induction current at the moment at which 

 circulation ceases, the interesting phenomenon of a rise in ar- 

 terial pressure may be observed, and cannot be explained other- 

 wise than by admitting with Stefani that the heart is capable, 

 under vagus stimulation, of charging itself with blood, even against 

 the pericardial pressure, which previously impeded this loading. 

 The vagus is thus able to excite active dilatation of the heart. 



Stefani applied the term diastolic pressure to that exerted by 

 the heart in diastole upon the surrounding fluid of the pericardium, 

 by which it overcomes the resistance, distends its cavities, and 

 permits the blood to penetrate it. He measured this diastolic 

 pressure in eight dogs, determining the difference between the 

 pressure in the pericardial cavity and in the vena cava. The 

 results are as follows : 



It appears from these figures that in ordinary diastole the 

 heart develops a pressure upon the pericardial fluid which is capable 

 on an average of supporting a column of water of 19 cm. This 

 result harmonises well with that obtained by the minimum 

 manometer of Goltz and Gaule as described above. 



On measuring the pericardial pressure capable of arresting the 

 circulation, before and comparatively soon after section of the vagi, 

 Stefani obtained the following results on five dogs : 



