448 



CIRCULATION OF BLOOD AND LYMPH. 



referred to in physiological literature are the spring manometer of 

 Fick* and the membrane manometer of Hiirthle.t 



The Fick manometer is shown in Fig. 182. It consists of a flat, hollow 

 metallic spring bent into the form of a C. The interior is filled with liquid 

 and is connected by rigid tubing, also filled with liquid, with the interior of 

 the artery. The variations of pressure in the artery are transmitted to the 

 interior of the spring and tend to straighten it, thus causing corresponding 

 movements of the free end. Before or after using this instrument it must be 

 calibrated, that is, the variations in movement must be given absolute values 

 in terms of millimeters of mercury by ascertaining directly the extent of move- 

 ment caused by known pressures. The Hiirthle manometer is more frequently 

 used at present. The principle made use of in this instrument is illustrated 

 by the diagram in Fig. 183. The instrument consists essentially of a small 

 box or tambour of very limited capacity; the top of the tambour is covered 



Fig. 182. The spring manometer of Fick (after Langendorff) : f, The flat metal 

 tube filled with liquid ; r, the lead tube connecting with the artery ; h, h, h, the lever 

 mechanism of light wood communicating the movements of / to the writing point, a; p, a 

 small disc immersed in a vessel of oil to still further dampen the inertia swings. 



with thin rubber dam and the cavity is filled with liquid and connected by 

 rigid tubing, also filled with liquid, with the interior of the artery or heart. 

 Variations in pressure in the artery are transmitted through the column of 

 liquid to the rubber membrane of the tambour, and the movements of this 

 latter are greatly magnified by a sensitive lever attached to it. The liquid 

 conduction and the small size of the tambour, which prevents any notice- 

 able outflow of liquid, combine to give a sensitive and very prompt record of 

 pressure changes. It is also necessary to calibrate this instrument whenever 

 used in order to give absolute values to the records obtained. A specimen 

 of a blood-pressure record obtained with this instrument is shown in Fig. 185. 

 It will be noticed that the size of the heart beat, relative to the distance from 

 the base line is much greater than in the record obtained with the mercury 

 manometer, Fig. 179. 



*Fick, "Archiv f. Physiologic," 1864, p. 583. 

 t "Archiv f. d. gesammte Physiologic," 49, 45, 



1891. 



