CIRCULATION. 129 



reached often below the pressure of the atmosphere. The pressure then 

 rises, perhaps continuing negative for a longer or shorter time, but presently 

 becoming equal to that of the atmosphere. Near this it continues, perhaps 

 with a gentle upward tendency, until, near the end of the ventricular diastole, 

 the rise becomes more rapid to the point at which the succeeding ventricular 

 systole is to begin. 



It is the course of the pressure between its rapid rise and its rapid fall which 

 has been the most disputed. The observers who employ manometers with liquid 

 transmission, have so far found that the high swift rise at the outset of the 

 systole is soon succeeded by a sudden change. According to them the pressure 

 within the manometer now exhibits fluctuations of greater or less extent which 

 are due, partly at least, to the inertia of the transmitting liquid ; but, with due 

 allowance made for these, the cardiac pressure is seen to maintain itself at a 

 high point throughout most of the systole until the rapid fall begins. During 

 this period of high pressure, the height about which the fluctuations occur may 

 remain nearly the same ; or this height may gradually increase, or gradually 

 decrease, up to the beginning of the rapid fall. As is shown by Figure 23, 

 this course of the systolic pressure causes its curve to bend alternately down- 

 ward and upward between the end of its greatest rise and the beginning of its 

 greatest fall ; but between these two points the general direction of the curve 

 approaches the horizontal, and therefore entitles this portion of it to the name 



12 3 4 



M ill i meters of 

 mercury. 



Line of atmospheric 

 pressure. 



Tenths of " second. 



Fig. 24.— Magnified curve of the course of pressure within the left ventricle of >li<- dog, the chest 

 being open; to be read from left to right. Recorded by the elastic manometer with transmission by air. 

 The crdinates have the following meaning: l, the closure of the mitral valve; 2, the opening oi the semi- 

 lunar valve ; 3, the closure of the semilunar valve; I, the opening of the mitral valve (von Fr< j i. 



of the " systolic plateau," a name which becomes more truly descriptive when 

 appropriate means are taken to eliminate the fluctuations due to inertia. The 

 best of the manometers with air transmission yields a curve ot* the pressure 

 within the ventricle which presents a different picture (Figs. 22 and 24). 

 The steeply rising line may diminish its steepness somewhat as it ascends, 

 but its rapid turn at the highest point of the curve is succeeded by no plateau. 

 The line simply describes a single peak, and begins the descent which marks 

 the rapid fall of pressure recognized by all observers. In these peaked curves 

 Vol. I.— 9 



