430 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



systole the heart pumps some blood out of this case, and shrinks as it does so, 

 thus tending to produce a vacuum ; in other words, to increase the amount of 

 negative pressure within the chest, and thus help to expand the swelling auri- 

 cles. Therefore for the suction which helps to charge the auricles during the 

 systole of the ventricles, that systole itself is partly responsible. 1 



Is the Auricle Emptied by its Systole ? Authorities differ still as to the 

 extent to which the auricle is emptied by its systole ; some holding the scarcely 

 probable view that, during this time, its contents are all, or nearly all, trans- 

 ferred to the ventricle ; 2 and others taking the widely different view that the 

 auricle actually continues to receive blood during its systole, which latter simply 

 increases the discharge into the ventricle. According to this latter opinion the 

 flow from the great veins into the auricle is absolutely unbroken. 3 All are 

 agreed, however, that the auricular appendix is the most completely emptied 

 portion of the chamber. 



Are the Venous Openings into the Auricle closed during its Systole ? 

 If not, does Blood then regurgitate, or enter ? As to these questions dif- 

 ferences of opinion are possible, because at the openings of the veins into the 

 auricle no valves exist which are effective in the adult, except at the mouth of 

 the coronary sinus. It is therefore a question, what happens at the mouths of 

 the veins during the auricular systole. These mouths are surrounded by rings 

 composed of the muscular fibres of the auricular wall ; and for some distance 

 from the heart the walls of some of the great veins are rich in circular fibres 

 of muscle. We have seen already (p. 407) that a rhythmic contraction of the 

 vense cavse and pulmonary veins occurs just before the systole of the auricles 

 and must accelerate the flow into the latter. Their swiftly following systole is 

 known to begin at the mouths of the great veins and from these to spread over 

 the rest of each auricle. It is evident at once that the circular fibres must 

 either narrow or obliterate, like sphincters, the mouths of the veins at the out- 

 set of the systole, and that these fibres thus take the place of valves. If the 

 closure be complete, all the blood ejected by the systole must enter the ventricle, 

 and a momentary standstill of blood and rise of pressure in the veins just with- 

 out the auricle must accompany its brief systole. A recent observer believes 

 the flow into the auricle to be interrupted even more than once during its cycle. 4 

 If the venous openings be not closed but only narrowed during the systole 

 of the auricles, the transfer of all or most of the ejected blood to the ventricle 

 must depend upon the pressure being lower therein than at the venous openings. 

 A slight regurgitation into the veins would, like the complete closing of their 

 mouths, cause a momentary checking of their blood-flow just without the auri- 

 cle, and a slight rise of pressure. Such a checking of the flow has in some 



1 A. Mosso : Die Diagnostik des Pulses, etc. Zweiter Theil : Ueber den negativen Puls, 

 p. 42. 



2 M. Foster: A Text-book of Physiology, New York, 1895, p. 182. 



3 Skoda : " Ueber die Function der Vorkammern des Herzens," Sitzungsberichte der mathem.- 

 naturw. Olasse der kais. Akademie der Wissenschaften in Wien, 1852, vol. ix. p. 788. L. Her- 

 mann : Lehrbuch der Physiologie, 1892, p. 66. 4 W. T. Porter: Op. tit., p. 534. 



