220 CIRCULATION OF THE BLOOD. 



3. The proximal arm of the manometer communicates at its 

 end, by means of along flexible tube (6) guarded by a clip, with 

 a " pressure bottle" containing solution of bicarbonate of soda. 

 A horizontal arm, which springs from it near the top, is con- 

 tinuous with the lead tube already mentioned. 



4. The manometer is fixed to the edge of the small mahogany 

 table on which the recording apparatus stands by means of 

 a brass clamp, which admits of its being raised or lowered at 

 will. The floating piston and rod (a} are made of black vul- 

 canite. The piston is in the form of an inverted cup, which 

 embraces the convex surface of the mercurial column. The 

 rod is quadrangular, and works in a guide, fixed at a height of 

 six inches above the upper end of the tube, by which it is kept 

 vertical. The writer, a fine sable miniature pencil, is supported 

 on the rod by a horizontal arm of thin wire, one-third of an inch 

 in length. One end of the wire is coiled round the rod, the 

 other round the stem of the pencil. From the guide just men- 

 tioned springs a horizontal arm, from which a silk plummet-line 

 is allowed to fall in such a way that it rests against the hori- 

 zontal part of the wire. By this means the point of the writer 

 is kept in constant contact with the paper, without exercising 

 too much pressure. 



6. The recording apparatus consists of a single cylinder, 

 which revolves at a constant rate of one revolution per minute. 

 The clock-work by which it is moved is constructed by Mr. 

 Hawksley on the model of the so-called u Foucault's Regula- 

 tor." To the right of the cylinder, as seen in the drawing, is 

 shown a large brass bobbin, of the same width as the cylinder, 

 on which a riband of paper is tightly rolled by machinery, of 

 sufficient length to serve for many hundred observations. 

 From the bobbin the paper riband is drawn off by the cylinder 

 as it revolves, against the surface of which it is accurately 

 applied, furnished with ivory friction wheels. 



34. Rules and Precautions to be observed in mak- 

 ing a Kymographic Observation. Before commencing, 

 it is necessary to see that the manometer is in proper order. 

 The mercury in the distal column must be clean and dry, and 

 the writing pencil moist and free from the remains of the ink. 

 To insure this, it should always be steeped in water after each 

 observation. 



To dry mercury, the best Swedish filtering paper is used. 

 It is cleaned by straining it through calico, or still better 

 through chamois leather. If the latter is used, it must be 

 strained under a considerable pressure. The system of tubes 

 communicating with the proximal limb of the manometer 

 must now be filled with solution of bicarbonate of soda. To 

 accomplish this, the arterial tube is first closed by a clip, and 

 the solution introduced with the aid of a pipette into the open 



