THE CIRCULATION OF THE BLOOD AND LYMPH 



passage towards the manometer, the maximum pressure attained in 

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

 able 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 50 mm. ; while in 

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

 25 mm. In the right auricle a maximum pressure of 20 mm. of 

 mercury has been recorded, and a minimum pressure of 10 mm. 

 or even less. But these results were obtained under somewhat 

 exceptional experimental conditions, and the normal maximum 

 pressures in the heart 

 cavities in man are prob- 

 ably not so high, especi- 

 ally in the right auricle 

 and ventricle. 



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 pres- 

 sure 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-curves of the 

 great arteries and great 

 veins. To obtain satis- 

 factory tracings of the 



swiftly-changing endocardiac pressure is a task of the highest tech- 

 nical difficulty, and it is only in very recent years that it has 

 been accomplished with any approach to accuracy by the use 

 of elastic manometers, in which the blood-pressure is counter- 

 balanced, not by the weight of a column of liquid, as in the mer- 

 curial manometer, but by the resistance to compression of a small 

 column of air or the tension of an elastic disc or of a spring. One 

 of the earliest of these was the now somewhat obsolete C-spring 

 manometer of Fick, of which a diagram is given in Fig. 25. Examples 

 of the most perfect elastic manometers of the modern type are the 

 improved instrument of Fick (Fig. 26), with the various modifications 

 it has undergone, and especially the manometers of Hiirthle. 



FIG. 25. 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. 



