86 A MANUAL OF PHYSIOLOGY 



Hiirthle's spring manometer consists of a small drum covered with 

 an indiarubber membrane, loosely arranged so as not to vibrate with 

 a period of its own. The drum is connected with the heart or with 

 a vessel, and the blood-pressure is transmitted to a steel spring by 

 means of a light metal disc fastened on the membrane. The spring 

 acts on a writing lever. The instrument is so constructed that for a 

 given change of pressure the quantity of liquid displaced is as small 

 as possible, and it is on this that its capacity to follow sudden 

 variations of pressure chiefly depends. The manometer is connected 

 with the cavity of the heart by an appropriately curved cannula of 

 metal or glass, which, after being filled with some liquid that prevents 

 coagulation (Practical Exercises, p. 195), is pushed through the 

 jugular vein into the right auricle or ventricle, or through the carotid 

 artery and aorta into the left ventricle. Some observers fill only 

 the cannula with fluid, and leave the capsule of the elastic manometer 

 and as much of the connections as possible full of air. Others fill 

 the whole system with liquid. And around the question of the 

 relative merits of ' transmission ' by liquid and by air has raged a 



FIG. 26. PICK'S ELASTIC MANOMETER. 



a, a is a metal piece tunnelled by a narrow canal of about i mm. in diameter 

 which enlarges below to a shallow saucer-shaped space b. The wide opening of b is 

 covered by a thin piece of indiarubber c, to the centre of which an ivory button d 

 is attached. The button presses on a strong steel spring /, which is attached at one 

 end to the brass frame e, e, and at the other, by means of an intermediate piece g, 

 to the lever h ; b is filled with a few drops of water, but the canal a contains only 

 air. When a is connected with the interior of the heart or of an artery, the changes 

 of pressure are transmitted to the spring, and recorded by the writing-point of the 

 lever. 



controversy which, however, now shows signs of coming to an end. 

 For there is reason to suppose that the character of the curves 

 obtained is modified among other circumstances by the manner in 

 which the pressure is transmitted. 



Thus, the pressure-curve of the ventricle, according to most 

 of those who have employed manometers with liquid trans- 

 mission and small inertia of the moving parts (Fig. 27), remains 

 after the first abrupt rise, which undoubtedly corresponds to 

 the ventricular systole, almost parallel to the abscissa line for a 

 considerable time, and then descends somewhat less suddenly than 

 it rose. This systolic ' plateau,' although usually broken by minor 

 heights and hollows, which may be partly due to inertia oscilla- 

 tions of the liquid or the recording apparatus, would indicate 



