210 



NEGATIVE PRESSURE. 



[BOOK i. 



left ventricle ; the unbroken line represents the course of the curve 

 when, the peripheral resistance being small, the pressure needed 

 to drive onward the blood is not very high, in the figure less than 

 150 mm. Hg. The dotted line represents the course of the curve 

 when, the peripheral resistance being great, the pressure is high, 

 in the figure nearly 200 mm. Hg. The lower curve is the curve of 

 pressure at the root of the aorta, the unbroken and the dotted 

 lines having the same significance as in the ventricular curve. 

 The line marks the commencement of the ventricular systole, 

 the line 1 the opening of the semilunar valves, and 3 the end 

 of the systole. The line 4 marks the beginning of what in dealing 

 with the pulse, we shall speak of as the dicrotic wave. The semi- 

 lunar valves are closed between 3 and 4 ; the closure is the result 

 at 3 of the cessation of the systole and as we shall see the cause 

 at 4 of the dicrotic wave of the pulse. The time is given in tenths 

 of a second. 



117. In many curves, as in some of those given above, the 

 pressure in the ventricle at the beginning of diastole falls not only 

 to the base line, which is the line of atmospheric pressure, but even 

 below it ; that is to say, becomes negative. Such a negative pressure 

 may be shewn by means of a minimum manometer, that is, a mano- 

 meter arranged so as to shew the lowest pressure which has been 

 reached in a series of events. The mercury manometer, which as we 



FIG. 56. THE MAXIMUM MANOMETER OF GOLTZ AND GAULE. 



At e a connection is made with the tube leading to the heart When the screw 

 clamp k is closed, the valve w comes into action, and the instrument, in the position 

 of the valve shewn in the figure, is a maximum manometer. By reversing the 

 direction of v it is converted into a minimum manometer. When k is opened, the 

 variations of pressure are conveyed along a, and the instrument then acts like an 

 ordinary manometer. 



