LECT. XVII. CIRCULATORY APPARATUS. 309 



LECTURE XVII. 



CIRCULATION OF BLOOD. 



AnGUMENT.^-Circulatory apparatus ; the heart; bloodvessels. Mechanism 

 of the circulation. The blood ; its general properties ; quantity in the 

 body. Number of pulsations. Velocity of the circulation ; experiments 

 of Hering, of Matteucci and Piria, of Poiseuille, and x>f Hales. Pressure 

 on the blood in the vessels; Poiseuille's hEemo-dynamometer ; results 

 obtained with it. Motion of the blood in the capillaries. Motive forces 

 of the circulation ; muscular contraction of the heart ; elastic contraction 

 of the arteries. Pulmonary circulation. Concluding observations. 



ONE of the most important effects of the nervous force is 

 the motion which it communicates to the blood in animals ; 

 for it is now admitted by all physiologists that muscular 

 contraction is the principal agent concerned in the circula- 

 tion of the blood. In order to carry out the intentions of 

 this course, I propose, in the present lecture, to demonstrate 

 to you that the apparatus which puts the blood in motion, 

 by muscular contraction, possesses all the conditions of an 

 hydraulic instrument; and I trust that I shall be able to 

 prove to you that the simplest and most elementary laws of 

 the movements of liquids are applied, to obtain, by the 

 passage of the blood through the various organs and dif- 

 ferent parts of the body, the numerous effects necessary to 

 the development and preservation of the animal. 



I regret that I am unable to treat of this subject in the 

 extended manner which it deserves, in consequence of 



