THE MECHANISM OF THE CIRCULATION. 



period of the second diastolic fall, like the period of ventricular 

 systole, remains almost constant. The second diastolic rise, E (Fig. 16), 



is no doubt produced by the 



A ^^^^^^^^^^^^^^^^^^^SW tilling of the auricles from 



the veins ; at the same time, 

 the intraventricular pressure 

 may rise above the tension of 

 the papillary muscles towards 

 the end of the systole, and 

 so again tend to drive the 

 auriculo - ventricular valves 

 out towards the auricular 

 cavity. The third diastolic 

 fall (F) is synchronous with 

 the relaxation of the ven- 

 tricle, and is due to the now 

 of blood from the auricle into 

 the ventricle. 



The time of the opening 

 and closing of the auriculo- 

 ventricular valves is obtained 

 by taking tracings of the 

 auricular and ventricular 

 pressures, simultaneously 

 with a differential trace re- 

 corded by the differential 

 manometer (see Fig. 17). 



The first diastolic rise (BC) 

 seen in Porter's auricular 

 curve (Fig. 16) has not been 

 found by all observers. 

 When this rise is obtained, 

 it must be due either to a 

 slight regurgitation or to the 

 ballooning out of the 



FIG. 17. 



Cardiac and aortic pressure curves (Porter) 



A, Contraction curve of the left auricular appendix. 



B, Differential tracing of the auricular and ventricular 



C, Ventricular pressure curve. 



D, Aortic pressure curve. 



The corresponding times are marked by ordinates, thus 

 ORDINATE 2. The pressure in the auricle and ventricle is 

 equal. An instant later the pressure is 

 higher in the ventricle, and the auriculo- 

 ventricular valves close. 



,, 3. There is marked here the beginning of the 

 aortic rise, that is to say, the moment 

 when the semilunar valves open. 



,, 4. This marks the bottom of the dicrotic notch. 

 At this point the semilunar valves close. 



,, 5. The auricular and ventricular pressures are 

 again equal, and immediately after the 

 valves open, as the auricular pressure rises 

 above the ventricular. 



aun- 



culo-ventricular valves. Owing to the great capacity of the veins, and 

 the absence of elastic tension of the venous wall, this rise is generally 

 not sufficient to produce a venous pulse. 



Observations on the maximal pressure in the auricle has yielded 

 very different results 



Chauveau and Marey estimated it as 2 '5 mm. Hg in the horse, right auricle. 

 Goltz and Gaule 20 ,, in the dog, 



Magini 20-22 



Porter 1-2 left auricle, 



v. Frey 10 right auricle. 



The pressure in the cavities of the heart is undoubtedly subject to 

 great variation. On what conditions these variations depend we have 

 as yet no exact knowledge. There is no reason to doubt the results of 

 the above observers, but further researches into the causes of the 

 variations are obviously needed. The fact of the thorax being opened 

 or closed, the efficiency or inefficiency of the vasomotor tone, the 



