44 A MANUAL OF VETERINARY PHYSIOLOGY 



systole. In Fig. 19 may be seen a venous pulse-tracing from the 

 dog in relation to auricular and ventricular contraction. The 

 information thus obtained regarding the condition of the auricle 

 is comparable with that obtained by the cardiograph and pulse- 

 tracing in relation to the condition of the ventricle. 



Intracardiac Pressures. — The positive and negative pressures 

 in the heart in large dogs have been measured with the following 

 results : 



Right auricle: maximum positive, 20 mm. (f inch) of mercury ; 



minimum negative, - 10 mm. (£ inch). 

 Left ventricle: maximum positive, 230 to 240 mm. {g\ to 



q£ inches) ; minimum negative, - 30 to 50 mm. (i\ to 



2 inches). 

 Right ventricle: maximum positive, 70 mm. (2| inches) ; 



minimum negative, -25 mm. (1 inch). 



Fig. 19. — Simultaneous Record of Jugular Pulse, Ventricular Con- 

 traction, Auricular Contraction, and Carotid Pulse, in the Dog 

 (cushny and grosh). 



a, c, v, the three elevations of the jugular pulse. (Time-trace, fifths of a 



second.) 



In the horse the maximum pressure in the left ventricle has 

 been found to be from 178 to 318 mm. of mercury (7 J to 12 1 

 inches), or a column of blood 2-4 to 4-3 metres (9 to 14 feet) in 

 height. In the right ventricle of the same animal the maximum 

 pressure was 34 mm. (i£ inches), equal to a column of blood 

 0-46 metre (1 \ feet) high. 



The negative pressure within the heart has not been satis- 

 factorily explained. According to one view, the heart behaves 

 like the bulb of a flexible syringe, which is discharged by pressure 

 and filled by the elastic dilatation of its own walls ; but there are 

 objections to this view, inasmuch as no elastic dilatation can be 

 demonstrated by experiment, nor have any of the other views 

 put forward been supplied by conclusive experimental evi- 

 dence. The explanation that the dilatation was due to the 



