206 PHYSIOLOGY CHAP. 



The diagram is so clear that a detailed description is super- 

 fluous. As appears in the figure, during presystole (which lasts 

 for about the sixth part of the time of the internal revolution) 

 there is a slight rise in auricular pressure which is transmitted to 

 the ventricle also, and which, as we shall see, effects the perfect 

 closure of the venous valve at the presystolic dead point. 



In systole (which lasts two and a half times longer than pre- 

 systole) two periods must be distinguished ; the first, which is 

 short, termed the period of tension or latent systole ; the second, 

 somewhat longer, that of efflux, or systolic evacuation. 



The first corresponds to the time necessary for the ventricular 

 pressure to reach and exceed the level of aortic pressure, in order 

 to determine the opening of the semilunars. 



With the sharp rise of ventricular pressure, there is a simul- 

 taneous rise of auricular pressure, determined by the tension and 

 upward propulsion of the cuspid valves. 



The duration of this period in the horse is, according to Marey, Ol " ; 

 Hurthlf, mi tlie contrary, finds it to lie for dog O02-O04 ", and Fredericq con- 

 firms this last figure. For man the data vary considerably. Marey, Rive, 

 Landois, Edgren give figures oscillating between (H " and O073", iGrnnmach 

 indicates a value of O07 ", Keyti O054". Hiirthle, on the ground of his 

 researches on the dog, calculates the period of tension as equal toO'03" for 

 man, a figure which is certainly too high. 



The second systolic period coincides with the rise of aortic 

 pressure (arterial pulse), the final elevation of ventricular pressure 

 which is then arrested in a kind of plateau, and a sudden drop of 

 auricular pressure, until it falls below zero, after which there is 

 again a slow but progressive rise. 



Physiologists have long disputed over that portion of the curve of intra- 

 ventricular pressure which is known as the systolic plateau, and corresponds 

 to the ventricular efflux. While the tracings obtained by Chauvean and 

 Marey in 1863 on the horse, and all the subsequent publications of Chauveau, 

 show an almost horizontal tract between the rapidly ascending (systolic), and 

 the corresponding and rapidly descending (diastolic), portions, many authors 

 maintain that the curve which represents the internal pressure of the 

 ventricle is composed solely of a rapidly rising, followed by a correspondingly 

 rapidly falling portion ; they deny the existence of the systolic plateau. This 

 point has recently been taken up again by various authors, both English and 

 American, among whom are Bayliss, Starling, and Porter. They have intro- 

 duced important technical alterations in the method, which tend to exclude 

 instrumental inertia. 



Bayliss and Starling employed a manometer containing a solution of 

 magnesium sulphate, one arm of which is open, and connected with the 

 cavity of the ventricle by means of an open sound, while the other arm 

 consists of a capillary tube sealed in the flame and containing air. This 

 small volume of air becomes more or less compressed by the liquid in the 

 manometer, owing to the pressure transmitted to it from the ventricle. The 

 degree of compression of the air column is registered by the displacement of 

 the shadow of the meniscus of the liquid column, which is projected on to a 

 rotating cylinder covered with sensitive paper. 



Porter invented a method with the same object, but too complicated to be 



