82 A MANUAL OF PHYSIOLOGY 



mercury, it does not readily follow rapid changes of pressure, and 

 the mercurial column, once displaced, continues for a time to 

 execute vibrations of its own, which are compounded with the true 

 oscillations of blood-pressure. But by introducing in the connection 

 between the manometer and the heart a valve so arranged as to 

 oppose the passage of blood towards the heart, while it favours its 

 passage towards the manometer, the maximum pressure attained in 

 the cardiac cavities during the cycle may be measured with con- 

 siderable accuracy. When the valve is reversed the apparatus 

 becomes a minimum manometer. In this way it has been found 

 that in large dogs the pressure in the left ventricle may rise as high 

 as 230 to 240 mm. of mercury, and sink as low as 30 to 40 mm. ; 

 while in the right ventricle it may be as much as 70 mm., and 



FIG. 21. DIAGRAM OF PICK'S C-SPRING MANOMETER. 

 A, hollow spring filled with alcohol. Its open end B is covered with a membrane and 

 is fixed to the upright F ; the other end C is free to move, and is connected with a 

 system of levers, which move the writing point D ; E is the cannula, which is connected 

 with the bloodvessel. When the pressure in the spring is increased it tends to straighten 

 itself. 



as little 35-25 mm. In the right auricle a maximum pressure of 

 20 mm. of mercury has been recorded. 



Our knowledge of the maximum and minimum pressure attained 

 in the cavities of the heart, even if it were far more precise than it 

 actually is, would only carry us a little way in the study of the endo- 

 cardiac pressure-curve, for it would merely tell us how far above the 

 base-line of atmospheric pressure the curve ascends, and how far 

 below the base-line it sinks. To exhaust the problem, we require to 

 have tracings of the exact form of the curve for each of the cavities 

 of the heart, and to know the time-relations of the curves so as to 

 be able to compare them with each other, and with the pressure- 



