CIRCULATION. 657 



kind referred to must be so difficult as to be must vary in different individuals from other 



almost useless; indeed, it is very probable circumstances besides a difference of stature, 



that some have mistaken the contraction for In the young, the quantity of blood is con- 



the dilatation, and we shall afterwards find sidered to be greatest. Of the whole of the 



that the power of suction, exerted by the heart blood contained in the body, it is estimated by 



on the blood, as measured by the force with Haller, and probably with accuracy, that four 



which the veins are emptied, is very small parts are contained in the arterial and nine in 



indeed. It is clear that the blood driven on the venous system. 



from behind by a propelling power, or flowing In endeavouring to estimate the quantity 



through parts which are pressed upon by of blood which passes through the heart in a 



neighbouring organs, must enter the heart given time, we must find the capacity of the 



more easily during the relaxation of the pa- cavities of the heart, we must ascertain whe- 



rietes of the ventricle than at any other period ther the cavities on the two sides are of the same 



during the heart's action, so as to give rise size, and, as it is almost impossible to measure 



to an appearance of suction, but direct expe- the quantity of blood evacuated from the heart 



riments make it sufficiently obvious that the at each stroke, we must find to what extent 



force of impulsion from behind is almost the the ventricles empty themselves during their 



sole cause of the entrance of the blood from systole. It is obvious that, so long as the 



the trunks of the great veins into the cavities circulation is uniform and no local accumu- 



of the heart. lation of blood takes place, the same quantity 



In order to form an estimate of the time in of blood must pass out of the ventricles into 



which a given quantity of blood may pass the larger arteries which enters by the veins, 



through the heart, or of the time in which the and for the same reasons, that the quantity of 



whole quantity of blood contained in the body blood passing through the right and left cavi- 



would take to pass through the heart, several ties of the heart must be exactly equal. The 



data are required which are not yet furnished circumstance that an equal quantity of blood 



by accurate experiments. In the first place, passes out of the right and left cavities of the 



we must know the average quantity of blood heart during their systole does not entitle us 



contained in the body, and, in the next place, to conclude that the capacity of the different 



the quantity which is evacuated from the heart auricles and ventricles is the same, because 



at each stroke or systole of the ventricles. any one of them during its systole may be 



With regard to the first of these points, more or less completely emptied than the rest, 



a number of calculations have been made and a regurgitation obviously takes place from 



which vary greatly in their results. Animals some of them, so that the whole blood which 



have been bled to death by the section of the they contain is not propelled in its onward 



larger bloodvessels, and the quantity of blood course. According to some anatomists the au- 



lost has been measured. The quantity of ricles are larger in capacity than the ventricles, 



blood lost in this way seems to have varied probably in the proportion of three or two and 



from l-10th to l-30th of the weight of the a half to two, and the auricles are by no means 



whole body, and Dr. Moulins, who formed completely emptied during their systole. An 



his estimates from experiments of this kind, opinion has very generally prevailed that the 



rated the quantity of blood in the human body cavities on the right side of the heart are some- 



at eight or nine Ibs. only, or l-20th of the what larger than those on the left. There is no 



weight of an average sized man, taken at 150 doubt that in making measurements of the re!a- 



or 160 Ibs. But it is obvious that when one of tive capacity of the two sides after death, it is 



the larger bloodvessels is opened, from the most frequently found so ; but it is obvious that 



suddenness of the flow, the animal faints or some have very much overrated the difference, 



dies before the whole or even a considerable and there is much reason to believe that the 



proportion of the blood has been lost; and it greater capacity of the right auricle and ven- 



has been ascertained from numerous obser- tricle depends in part on the accumulation of 



vations, that when the blood flows more gra- blood which generally takes place in most 



dually and from small vessels, as occurs in kinds of slow death in the pulmonary arteries, 



hemorrhages from the nose, stomach, rectum, and in part also upon the greater thinness and 



or uterus, a proportionally much greater quan- consequent distensibility of the right ventricle, 



tity of blood may be lost than occasions death In men dying suddenly, and in animals killed 



in animals experimented upon by the section purposely, in which the pulmonary artery is 



of the larger arteries or veins. Instances are opened so as to allow of the free egress of the 



on record in which from ten to twenty Ibs. blood from the right side of the heart, the 



and even greater quantities of blood have capacity of this ventricle is not greater than 



flowed from the human body within twenty- that of the left, and the proportions of the 



four hours.* We feel inclined on these capacity of the two sides of the heart usually 



grounds to coincide with the estimate formed found after slow death are sometimes reversed 



by Haller, that the blood forms about a fifth of when a ligature is placed on the aorta and the 



the weight of the body, or equals from twenty- pulmonary artery is opened.* Most authors 



five to thirty Ibs. in a man of the average seem to have agreed to follow the estimate of 



weight of 150 Ibs. It is obvious that this the capacity of the ventricles given by Hales 



in his Medical Statics. This author esti- 



Scc Haller's Elementa, and Kcill on the An. 



Econ. * Sabatier. 



