150 ENDO-CARDIAC 2>RESSUPE. [BOOK i. 



Hence we may infer, and the conclusion may be supported by other 

 arguments, that at the actual closure of the semilunar valves, 

 giving rise to the second sound, the ventricle has just finished its 

 systole and is beginning to relax. If this view be correct the time 

 of the closure of the valves is not indicated on the cardiographic 

 tracing by any special mark, but coincides with the commencement 

 of the more sudden and final fall of the lever as at d in Fig. 24. 



Marey thought that the oscillations seen at d' in his curves and 

 obvious in the auricle and cardiac impulse as well, were due to 

 oscillations of the auriculo-ventricular valve, but in that case they 

 would be inverted in the auricular curve; whereas they are not. 

 It is difficult to say what gives rise to them. We may repeat that 

 many of the details of these curves vary considerably even with the 

 same method of investigation and when the same apparatus is 

 employed. In all probability the character and sequence of the 

 events are modified by various circumstances, such as the rate and 

 rapidity of the beat, the quantity of blood flowing into the heart, 

 and the pressure obtaining in the arteries. 



Amount of Pressure. Although the instrument of Chauveau 

 and Marey may be experimentally graduated and has been used 

 to measure the amount of pressure in the several cavities of the 

 heart, it is, as we have said, open to objections. Better results may 

 be gained by passing through the jugular vein into the right auricle 

 and thence into the right ventricle, or through the carotid artery 

 into the left ventricle, a tube open at the end introduced into the 

 heart and connected at the other end with a manometer. Varia- 

 tions of pressure in the cardiac cavities are thus transmitted di- 

 rectly to the mercury column of the manometer in the same way 

 as those of an artery when arterial pressure is measured. The 

 inertia of the mercury column however prevents an exact response 

 to the rapid movements of the heart, and obscures the results ; 

 though by using maximum and minimum manometers, the 

 maximum and minimum pressures of the several cavities may be 

 determined. 



The principle of the maximum manometer, Fig. 25, consists in the 

 introduction into the tube leading from the heart to the mercury 

 column, of a (modified cup-and-ball) valve, opening, like the aortic 

 semilunar valves, easily from the heart, but closing firmly when fluid 

 attempts to return to the heart. By reversing the direction of the 

 valve, the manometer is converted from a maximum into a minimum 

 instrument. When an ordinary manometer is connected with a ven- 

 tricular cavity, the movements of the mercury do not follow exactly the 

 rapid variations of pressure of the cavity, and the height of the column 

 fails to indicate both the highest and the lowest pressures. 



In this way in the dog a maximum pressure has been observed 

 in the left ventricle of about 140 mm. (mercury), in the right 

 ventricle of about 60 mm. and in the right auricle of about 20 mm. 



