286 TEXT-BOOK OF PHYSIOLOGY 



blood is discharged into the aorta. As the discharge of blood comes to 

 an end, the systolic pressure gradually falls as does the intra-ventricular 

 pressure. With the sudden onset of the ventricular relaxation the intra- 

 ventricular pressure suddenly falls whereupon the semilunar valves are 

 closed by the backward movement of the blood under the elastic recoil 

 of the arterial walls. 



In accordance with the foregoing: the ventricular systole may be sub- 

 divided into two periods: 



1. The period of rising tension, from the beginning of the systole and the 



closure of the auriculo-ventricular valves to the opening of the semi- 

 lunar valves, the pre-sphygmic period. 



2. The period of discharge, the sphygmic- period, from the opening of the 



semilunar valves to the end of the systole. 

 The ventricular diastole may also be divided into two periods: 



1. The period of falling tension or relaxation, the post-sphygmic period, 



from the end of the systole and the closure of the semilunar valves to 

 the opening of the auriculo-ventricular valves. 



2. The period of filling, from the opening of the auriculo-ventricular valves 



to the beginning of the succeeding auricular systole. 

 The Time Relations of the Successive Periods of the Ventricular 

 Activity of the Human Heart. The duration of each of the periods of 

 ventricular activity as stated in the foregoing paragraph will vary 

 somewhat with the animal as well as with the rate of the heart 

 during the time of the experiment. In human beings the same holds 

 true. As the outcome of different methods of investigation the average 

 duration of each period in man has been approximately estimated as 

 follows : 



Period. Rate 70. Rate 80. 



1. Presphygmic 0.055 1 Systole 0.051 1 Systole 



2. Sphygmic 0.268 ( 0.323 0.254^0.305 



3. Post-sphygmic 0.050 1 Diastole . 0.050 1 Diastole 



4. Pause 0.490/0.540 0.395/0.445 



Total Duration 0.863 -75 



The Intra-auricular Pressure. During the auricular systole the 

 pressure within the auricle undergoes variations as shown by direct examina- 

 tion by means of a cannula inserted into the auricular cavity and connected 

 externally with a recording tambour, or by indirect examination by means 

 of an exploratory tambour placed over the right jugular vein in close relation 

 to the clavicle. The pressure variations in the jugular vein which are thus 

 recorded by means of a tambour provided with a writing lever are believed 

 to be caused by, closely follow and reproduce the pressure variations in the 

 auricle. 



Among the most important of the direct examinations of the auricular 

 pressure are those of Porter, carried out by the insertion of a large cannula in 

 the auricular appendix, or in a pulmonary vein close to the auricle and con- 

 nected by its free extremity with a Hurthle tambour. The curve of pressure 

 thus obtained, shown in Fig. 123, is characterized by three positive and three 

 negative waves. Among the more important of the indirect determinations 

 of the auricular pressure variations are those of Bachmann, carried out with 

 highly sensitive recording tambours. The curve of pressure variations in 



