THE PHENOMENA NOTED DURING EACH CARDIAC CYCLE 297 



The manometers designed by O. Frank ^ do not differ materially from those 

 devised by Hiirthle. The principle involved in their construction is that the mass 

 of liquid actually moved for the purpose of transferring the blood pressure, must 

 be as small as possible, otherwise the momentum of the different parts of the instru- 

 ment may give rise to vibrations which are not at all in keeping with the conditions 

 as they actually are. The tendency to " af ter-vibrate, " Frank has sought to 

 mitigate by making the connecting tube between the blood-vessel and the man- 

 ometer as large and as short as possible, while the orifice carrying the recording 

 membrane is reduced to the smallest size practicable (Fig. 152). The frequency 

 of vibration of this instrument is extremely great and hence its power of accurately 

 following the variations in pressure cannot be doubted. Without desiring to enter 

 into a detailed discussion of the theory of manometers, it may be stated that 

 Hiirthle does not regard the principle as put down by O. Frank as physically 

 sound. 2 Naturally, the greatest sensitiveness is attained by the reflecting or optical 

 manometer. The membrane of this instrument is not weighted by a writing lever 

 with its different adjustments, but is equipped solely with a very small mirror 



n") 



Fig. 152. — Diagram of Frank's Membrane Manometer. 

 K, for attachment of cannula inserted in blood vessel; hde, connecting piece of 

 manometer filled with sodium carbonate solution; cf, connections for flushing out the 

 system; S, membrane; S, mirror riding upon membrane. 



from which a beam of light is reflected against a screen. In this way, the oscilla- 

 tions of the membrane may also be transferred upon the sensitive paper of a camera 

 moved with a certain rapidity 



The Intra-Auricular Pressure and the Function of the Auricles. — 



If the cavity of the right auricle of a dog is connected with a maxi- 

 mal-minimal valve and with a mercury manometer, it will be found to 

 produce a systolic pressure of about 20 mm. Hg. and a diastolic pressure 

 of — 10 to —20 mm. Hg.^ The total change in pressure in this cham- 

 ber, therefore, amounts to 30 or 40 mm. Hg. during each cardiac cycle. 

 Very similar conditions prevail in the left auricle. It may be stated 

 at this time that the negative pressure encountered in these cavities, 

 as well as in the central venous trunks, is not developed actively, but 

 is dependent upon the aspiratory action of the tissue of the lungs. 

 These organs exert an elastic pull upon the relatively soft walls of these 



1 Zeitschr. fiir Biologie, 1910, 53. 

 ^Pflliger's Archiv, cxxxvii, 1911, 225. 

 3 Goltz and Gaule, ibid., xvii, 1878, 100. 



