CHAP, iv.] THE VASCULAR MECHANISM. 



151 



Marey had previously, by means of his own instrument, determined 

 the pressure in the horse to be in the left ventricle about 150mm., 

 in the right ventricle only about 30 mm., while that of the right 

 auricle he estimated at not more than a few mm. 



FIG. 25. 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 v 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. 



It is interesting to observe that the minimum pressure may 

 fall below that of the atmosphere : thus in the left ventricle (of 

 the dog) a minimum pressure varying from 52 to 20 mm. may 

 be reached, the minimum of the right ventricle being from 17 to 

 16 mm., and of the right auricle from 12 to 7 mm. 1 Part of 

 this diminution of pressure in the cardiac cavities may be due, as 

 will be explained in a later part of this work, to the aspiration of 

 the thorax in the respiratory movements. But even when the 

 thorax is opened, and artificial respiration kept up, under which 

 circumstances no such aspiration takes place, the pressure in the 

 left ventricle may still sink as low as 24 mm. The minimum ma- 

 nometer, which shews most distinctly the existence of this negative 

 pressure, obviously gives no information as to the exact phase of 

 the beat in which it occurs ; and there is some difference of opinion 

 as to the exact time at which it takes place. Goltz and Gaule, to 



1 These numbers are to be considered merely as instances which have been 

 observed, and not as averages drawn from a large number of cases. 



