. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative. THE CIRCULATION OF THK BLOOD. 243 the nature of arterial tracings, it is important that the circum- stances under which they are obtained should be FiQ. 206.—Marey's improved sphygmograph arranged for taking a tracing. A, steel spring; B, first lever; C, vpriting lever; C'^ its free writing end; 2), screw for bringing B in contact with C; G, slide with smoked paper; H, clock-work; i, screw for increasing the pressure; M^ dial indicating the amount of pre
. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative. THE CIRCULATION OF THK BLOOD. 243 the nature of arterial tracings, it is important that the circum- stances under which they are obtained should be FiQ. 206.—Marey's improved sphygmograph arranged for taking a tracing. A, steel spring; B, first lever; C, vpriting lever; C'^ its free writing end; 2), screw for bringing B in contact with C; G, slide with smoked paper; H, clock-work; i, screw for increasing the pressure; M^ dial indicating the amount of pressure, K, K, straps for fixmg the instrument to the ai-m, and the latter to the double- inclined plane or support {Byrom Bramwell). The movements of the vessel wall in most mammals suitable for experiment and in man is so slight that it becomes necessary to exaggerate them in the tracing, hence long levers are used to accomplish this. The sphygmograph is the usual form of instrument em- ployed for the purpose. It consists, essentially, of a clock-work for moving a smoked surface (mica plate commonly) on which the movements of a lever-tip, answering to those of a button placed on the artery, are recorded. We shall do well to in- quire whether there are any features in common in trac- ings obtained jn various ways, and which have there- FiQ. 207.—Diagrammatic schema showing the essential part of the instrument when in working order. The knife-edge B" of the short lever is in contact with the writing-lever C. Every movement of the steel spring at A", communicated by the arteries, will be imparted to the writing- lever (Byrom Bramwell). fore in all probability a real foundation in nature. An inspection of a large number of pulse-tracings, taken un- der diverse conditions, seems to show that in all of them there occurs, more or less marked, the following : 1. An upward. Please note that these images are extracted from scanned page images that may have been digitally en
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