CIRCULATION OF THE BLOOD. THE PULSE. _ _4i 



42. . And 9th. and finally, that in the capillary terminations of 

 the system of canals formed by the aorta, the arterial blood acts 

 upon the organs, is changed there into venous blood, and enters 

 the veins to be carried again to the heart. 



13. In accomplishing the circulatory circle, the blood then 

 passes twice through the heart, in the state of venous blood on 

 the right side, and in the state of arterial blood in the left side 

 of this organ ; (page 36. Jig. 5. fy page 42. jig. 8.) yet, the cir- 

 culation is complete, because the pulmonary and aortic cavities 

 of the heart do not open one into the other, and the venous 

 blood passes through the entire respiratory apparatus to be 

 transmuted into arterial blood. 



44 The mechanism by which the blood moves through these 

 vessels is easily understood. The cavities of the heart contract 

 and enlarge alternately, and by contracting they force the blood 

 into the canals with which they (the cavities) are in communica- 

 tion. 



45. The two ventricles contract at the same time, and while 

 their sides or parietes relax, the auricles in their turn contract. 



46. The movement of contraction bears the name of systo/e, 

 and the term diaatufa is applied to the opposite movement, or 

 dilatation. 



47. The beating or pulsation of the heart is very frequent ; in 

 man of adult age it takes place from sixty to seventy-five times 

 in a minute ; in old men the number of beats is a little increased, 

 and in very young infants it is generally about one hundred and 

 twenty. But a variety of circumstances may influence both the 

 frequency and force of the beats of the heart; they are accelerated 

 by exercise, by moral emotions, and by a great number of dis- 

 eases; in swooning or syncope, they are considerably diminished, 

 or even completely interrupted. 



48. The left ventricle in dilating fills with blood, and in con- 

 tracting afterwards, forces out the liquid which it contains. 



49. This ventricle communicates only with the left auricle by 

 an opening called the aitricnlo-crtitricnlar opening, and with the 



42. Where is the arterial changed into venous blood ? 



43. In accomplishing its entire circle, how many times does the blood 

 pass through the heart? 



44 What cause* the blood to move in the blood vessels ? 



45. Do the auricles and ventricles >f the heart contract at the same time? 



46. What is the contraction of the heart called ? What is its dilation called ? 



47. What is the frequency of the heart's pulsation? Is it most frequent 

 in infants or in old men? What circumstances influence the frequency o. 

 the heart's pulsation ? 



4rf. When the left ventricle dilates, what happens ? 

 49. With what does the left ventricle communicate? 

 4 



