100 CIRCULATION 



for both ventricles making the total work of the heart equal 

 to 288 grammeters of work. Practically all the energy of the 

 heart's contractions is converted into heat by the friction of 

 the blood in the vessels. 



By the employment of maximum and minimum manometers 

 it has been ascertained upon a dog in one case that the maxi- 

 mum pressure in the ventricle rose as high as 234 mm. Hg, 

 while that in the aorta reached 212 mm. Hg. The minimum 

 of the left ventricle was minus 38 mm. Hg, while that of the 

 aorta did not get lower than 120 mm. Hg. These values vary, 

 but their relations to one another may be taken as an example 

 of what is true of both ventricles. It is seen that the pressure 

 in the artery is always high, fluctuating but little, while that 

 of the ventricles rises above the highest arterial pressure and 

 falls much below. The pressure of the blood in the ventricle 

 must overcome that within the artery to open the semilunar 

 valves and force the blood into the artery. As the pressure 

 falls in the ventricle the semilunar valves close as soon as it 

 is less than that of the artery, and prevent regurgitation. 

 When the pressure in the ventricles is at its lowest, the blood 

 streams in from the large veins and from the auricles, because 

 the pressure in the latter, although low, is higher than that 

 in the ventricle. 



Curves of endocardiac pressure which are obtained by insert- 

 ing a hollow probe into the ventricles of the heart give a curve, 

 characterized by a plateau, i. e., the pressure instead of falling 

 after reaching a maximum is sustained for some time (Fig. 2). 

 The fluctuations of the plateau are due to oscillations produced 

 by inertia. An endocardiac pressure curve very rarely shows 

 any indication as to the play of valves'. These must be obtained 

 by carefully graduating two elastic manometers and connecting 

 them with auricle and ventricle, or ventricle and aorta respec- 

 tively. The relative pressures are given by the heights to which 

 the recording levers rise, and thus the closure of the various 

 valves may be ascertained. As long as the tricuspid or mitral 

 valves are open the pressure in the ventricle is lower than 

 that in the auricle, and the blood is entering from the veins. 

 That in the arteries is shut out by the closed semilunar valves. 

 This is called r th period oflrevepticn of the bl'ood. When the 

 cuspid valveS kresnuV the scmiluna*- valves are open, and the 



