CHANGES OF PRESSURE DURING CARDIAC CYCLE. 17 



simple valve. An instrument so constructed is shown in Fig. 8. If C be 

 placed in connection with the intracardiac cannula, A acts as a minimal, 

 and B as a maximal manometer. 



Using Hiirthle's spring manometer in conjunction with maximal and 

 minimal manometers, we can arrive at the true changes of intracardiac pressure, 

 for the first will give us the time, sign, and velocity, and approximately the 

 amount of the pressure variations, while the last will give us the true maximal 

 and minimal pressures. 



The sphygmoscope of Chauveau and Marey, as modified by Fredericq, is 



FIG. 9. Diagram of Fredericq's sphyg- 

 moscope. a, cannula ; b, rubber finger 

 stall ; c, cork ; d, lever of tambour. 



FIG. 10. Diagram of v. Basch's hollow 

 spring manometer. The index records 

 the pressure on a graduated scale. A 

 recording style can be affixed to the end 

 of the hollow C-spring. 



probably as perfect an instrument as the Hiirthle manometer, and is far 

 simpler in construction. 1 



The end of a rubber finger-stall is drawn over the end of a rubber cork, 

 and a glass tube connected with the intracardiac cannula passes through the 

 rubber cork into a very small air space, which is left beneath the apex of 

 the finger-stall at the top of the cork. The cork is inserted into the end of a 

 glass thistle-shaped funnel, and this is in its turn connected with a delicate 

 Marey tambour. Every part of the instrument is reduced to the smallest 



FIG. 11. Hiirthle's differential manometer. 



dimensions, and the rubber tip of the finger-stall acts as an elastic counterpoise 

 to the variations of pressure. 



One of the most convenient forms of manometer for accurate work is that 

 of v. Basch, who has constructed a C-spring manometer on the smallest 

 possible scale. The advantages of this instrument are, that a permanent 

 hollow spring replaces a tambour covered with a perishable rubber membrane, 



1 Fredericq, "Manipulations de physiologic," Paris, 1892, p. 174. 

 VOL. II. 2 



