May 12, 1905.] 



SCIENCE. 



753 



The pressure in the ventricle is varied 

 through a tambour covered with rubber mem- 

 brane. The membrane is grasped between two 

 disks, one below and one above. The upper 

 disk is screwed down upon the lower until the 

 membrane is tightly held. To these disks is 

 fastened a rod which ends in a yoke. The 

 yoke rests upon a small wheel, which in turn 

 is supported by a brass plate eccentric in form. 

 This brass plate is revolved by turning a 

 handle attached to the axle. As the plate re- 

 volves the small wheel bears upon the eccen- 



tric rim and rises and falls with the rise and 

 fall in the rim of the plate. The motion of 

 the small wheel is transferred through the 

 yoke, rod and disk to the rubber membrane 

 and thus to the interior of the ventricle. 



The rim of the eccentric brass plate repro- 

 duces the intraventricular pressure curve in 

 the dog. In projecting this curve upon the 

 plate the periphery is divided into fractions 

 of a second and the radii are divided into 

 millimeters of mercury pressure. 



Each revolution of the eccentric plate re- 

 produces in the ventricular tube both the time 

 and the pressure relations of the ventricular 

 cycle in the dog. The intraventricular pres- 

 sure curve may be written by connecting the 

 side tube with a membrane manometer, and 



clamping oQ the arterial mercury manometer 

 to be mentioned shortly. 



When the pressure rises in the ventricle to 

 a sufficient height the contents of the ventricle 

 will be discharged through the aortic valve 

 into the aorta, and thus (through a convenient 

 metal tube) into the arterial tube, leading to 

 the capillary resistance. Here two paths may 

 be taken : the liquid may pass either through 

 the capillary channels in the cane, thus meet- 

 ing with a high resistance, or this resistance 

 may be lessened to any desired degree by un- 

 screwing a clamp and thus opening the side 

 tube. Both paths lead to the venous tubes, 

 whence the liquid passes through the mitral 

 valve into the ventricle. The mitral and 

 aortic valves are of a modified Williams type. 

 Metal tubes closed at one end conduct the 

 liquid respectively to or from the ventricle. 

 The liquid enters or leaves the valve tube 

 through a hole covered by a rubber valve-flap, 

 not shown in Fig. 1. Each valve is sur- 

 rounded by a glass tube through which the 

 working of the valve may be inspected. 



Mercury manometers measure the pressure 

 in the arteries and veins near the capillary 

 resistance. The arterial manometer is pro- 

 vided with a glass thistle-tube to catch any 

 mercury that may be driven out by a careless 

 operator. 



If the arterial mercury manometer be re- 

 placed by a membrane manometer, or if it be 

 provided with a float and writing-point ar- 

 terial pressure curves may be written, iden- 

 tical with those obtained from the carotid 

 artery of the dog. 



Normal sphygmographic tracings may be 

 obtained by using a sphygmograph on the 

 aortic tube. 



Palpation of the arterial tube will give a 

 pulse the ' feel ' of which can not be distin- 

 guished from that of the pulse in the normal 

 subject ; the pressure waves in the quantitative 

 scheme and in the living animal are identical 

 in respect of both time and pressure. 



W. T. Porter. 



Harvakd IVIedical School. 



ROCKING KEY WITH METAL CONTACTS. 



The instrument illustrated by the figure 

 serves as a simple key, short-circuiting key. 



