CIRCULATION. 



Tliis may be called the "period of reception of blood." During the greater 

 part of the period when the cuspid valve is shut, the arterial valve is open ; 

 the pressure is higher in the ventricle than in the artery ; and the ejection 

 of blood from the former is taking place. This may be called the " period 

 of ejection," and lies in Figures 108 and 109 between the ordinates 2 and 

 3. The careful work which has enabled us to mark the valve-play upon 

 the ventricular curve has demonstrated the interesting fact that there occur 

 two brief periods during each of which both valves are shut, and the ven- 

 tricle is a closed cavity. Of these two periods, one immediately precedes the 

 period of ejection, and the other immediately follows it. The first lies, in 

 Figures 108 and 109, between the ordinates 1 and 2 ; the second, between 3 

 and 4. The explanation of these two periods is simple. It takes a brief but 

 measurable time for the cardiac muscle, forcibly contracting upon the impris- 

 oned liquid contents of the closed ventricle, to raise the pressure to the high 

 point required to overcome the opposing pressure within the artery and to open 

 the semilunar valve. Again, it takes a measurable time, probably seldom 

 quite so brief as the period just discussed, for the cardiac muscle to relax suffi- 

 ciently to permit the pressure in the closed ventricle to fall to the low point 

 required for the opening of the cuspid valve. The ventricular cycle, thus 

 studied, falls into four periods : the first is a brief period of complete closure 

 with swiftly rising pressure ; the second is the period of ejection, relatively 

 long, and but little variable ; the third is a period of complete closure, with 

 swiftly falling pressure ; the fourth is the period when the pressure is low and 

 blood is entering the ventricle. This last period is very variable in length, 

 but at the average pulse-rate it is the longest period of all. 



Phenomena of the Period of Reception of Blood. We have already 

 followed the course of the pressure within the ventricle from the moment of 

 opening of the auriculo- ventricular valve to that of its closing (p. 416). 

 During this time the ventricle is receiving its charge of blood, the flaccidity of 

 the wall rendering expansion easy and keeping the pressure low. The blood 

 which enters first has been accumulating in the auricle since the closing of the 

 cuspid valve, and now, upon the opening of this, it both flows and is to some 

 slight degree drawn into the ventricle. This blood is followed by that which, 

 during the remainder of the " repose of the whole heart," moves through the veins 

 and the auricle into the ventricle under the influence of the arterial recoil and 

 the other forces which cause the venous flow (p. 397) ; and the charge of the 

 ventricle is completed by the blood which is injected at the auricular systole. 



The Negative Pressure within the Ventricles. That the heart, in its 

 diastole, draws something from without into itself is a very ancient belief, and 

 this mode of its working played a great part in the doctrines of Galen and of 

 the Middle Ages. In 1543, Vesalius, who, on anatomical grounds, questioned 

 some of Galen's views as to the cardiac physiology, fully accepted this one. 1 



1 Andrew Vesalii Bntirellensts, Scholce mtiticorum Patavin<r proh.^ori^ tic Ifitmam corporis 

 fabrica Libri septan. Basile^, ex officina loannis Oporini, Anno Salutis reparatjv MDXLIII. 

 Page 587. 



