CHAP, iv.] THE VASCULAR MECHANISM. 



239 



column to a corresponding height. Since this column, once past the 

 valve, cannot return, the mercury remains at the height to which it was 

 raised by it and thus records the maximum pressure. By reversing 

 the direction of the valve, the manometer is converted from a maximum 

 into a minimum instrument. 



FIG. 36. 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. 



The maximum manometer applied to the cavity of either 

 ventricle or of the right auricle, gives a record of the highest 

 pressure reached within that cavity, and the minimum manometer 

 similarly applied shews the lowest pressure reached, during the 

 time that the instrument is applied. 



The maximum manometer thus employed shews that the 

 maximum pressure in the left ventricle is distinctly greater than 

 the mean pressure in the aorta (the ordinary mercury manometer 

 having previously given the paradoxical result, due to the inertia 

 of the mercury, that the mean pressure in the left ventricle might 

 be less than in the aorta), that the maximum pressure in the right 

 ventricle is less than in the left, and in the right auricle is still 

 less. In the dog for example the pressure in the left ventricle 

 reaches a maximum of about 140 mm. (mercury), in the right 

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



But the chief interest attaches to the minimum pressure 

 observed ; for the minimum manometer records a negative pressure 



