LECT. XVII. PULMONARY CIRCULATION. 331 



walls of the left ventricle thus approach each other, con- 

 tract with a great rapidity, which can be determined when 

 we know the exact duration of the contraction and the 

 quantity of blood expelled. The capacity of the ventricle 

 is thus diminished, and a certain quantity of blood thrown 

 into the aorta, and a movement communicated to it which 

 is propagated throughout the system. At the instant that 

 the arteries dilate, the right ventricle opens, and the blood 

 enters it. The contraction of the left ventricle ceasing, the 

 arteries return to their original condition, and again propel 

 the bloo d forward. 



Pulmonary Circulation. We have passed over in silence 

 all that which relates to the pulmonary circulation, this 

 being produced by the same causes, and under the same 

 laws as the circulation in the rest of the body. 



Conclusion. Thus, then, by the arrangement of the 

 various parts of the sanguineous system, is solved, by a 

 very simple mechanism, and conformably to the physical 

 laws of the movements of fluids, a very complicated hy- 

 draulic problem : namely, that of the continued distribution 

 of the same liquid in a system of tubes, having different 

 diameters in different parts of the body, and, consequently, 

 with very variable velocities, and always in relation to the 

 functions of these parts, and all this by the simple alternating 

 impulsion given to this fluid by the sudden contraction of a 

 species of sac, which makes a part of the tube itself. 



