ACTION OF THE VALVES. 199 



By first subjecting the bags to known degrees of pressure, 

 the degree of elevation of a lever may be graduated so as to 

 represent the degrees of the cardiometer. In analyzing traces 

 made by the left ventricle, right ventricle, and right auricle, 

 in the horse, Marey found that, as a general rule, the 

 comparative force of the right and left ventricles is as 1 to 3. 1 

 The force of the right auricle is comparatively insignifi- 

 cant, being in one case, as compared with the right ventricle, 

 only as 1 to 10. 



Action of the Valves. We have already indicated the 

 course of the blood through the cavities of the heart, and it 

 has been apparent that the necessities of the circulation de- 

 mand some arrangement by which the current shall always 

 be in one direction. The anatomy of the valves which guard 

 the orifices of the ventricles gives an idea of their function ; but 

 we have yet to consider the precise mechanism by which they 

 are opened and closed, and the way in which regurgitation is 

 prevented. 



In man and the warm-blooded animals, there are no 

 valves at the orifices by which the veins open into the auri- 

 cles. As has already been seen, compared with the ventri- 

 cles, the force of the auricles is insignificant; and it has 

 furthermore been shown by experiment that the ventricles 

 may be filled with blood, and the circulation continue, when 

 the auricles are entirely passive. Though their orifices are 

 not provided with valves, the circular arrangement of the 

 fibres about the veins is such, that during the contraction 

 of the auricles the openings are materially narrowed, and re- 

 gurgitation cannot take place to any great extent. The force 

 of the blood flowing into the auricles likewise offers an obsta- 

 cle to its return. There is really no valvular apparatus which 

 operates to prevent regurgitation from the heart into the 

 veins ; for the valvular folds which are so numerous in the 



1 MAREY, op. cit. y p. 104. 



