139 



DEMONSTRATIONS 

 RELATING TO THE FUNDAMENTAL PHENOMENA 



OF 



CIRCULATION AND RESPIRATION, 



AND TO THE 



ELECTROMOTIVE PROPERTIES OF MUSCLE. 



I. Mode of Measuring and Recording the Arterial Pressure. Use 

 of Recording Apparatus. 



The instrument used is called a kymograph (see p. 61). The arterial 

 cannula is a T-shaped tube of glass. By its stem, it is connected with the 

 manometer (a U-shaped glass tube containing mercury). One branch of the 

 T is drawn out and bevelled so as to be easily introduced into the artery : to 

 the other is fitted a short piece of indiarubber tubing, guarded by a steel clip. 

 The stem of the cannula communicates with the proximal arm of the mano- 

 meter by an unyielding tube of lead or guttapercha. The proximal arm (that 

 connected with the cannula) also communicates by a long flexible tube with a 

 bottle containing solution of bicarbonate of sodium under pressure. The mano- 

 meter is fixed to the recording apparatus, so that its oscillations are inscribed on 

 the moving surface. This is effected by means of a style carried by a vulcanite 

 rod, which floats on the surface of the mercury in the distal (open) limb of the 

 manometer. The recording cylinder is driven by clockwork : it is either 

 covered with smoked glazed paper, or is fed by an endless roll of paper, in 

 which case a sable pencil, charged with coloured ink, is substituted for the 

 style. The paper surface in either case moves at a uniform] rate of 20 inches 

 per minute. 



The artery used is the carotid of the rabbit. The distal end of the prepared 

 part of the vessel is ligatured. The proximal end is temporarily closed by a 

 spring-clip. The vessel having been opened near the ligature, the cannula 

 is introduced and secured in its place by a second ligature, its drawn-out 

 end being directed towards the heart. This done, the guttapercha tube of 

 the manometer is connected with the stem of the cannula, and the whole 

 system filled with solution of sodic bicarbonate under a pressure of about 

 four inches of mercury. On removing the clip on the artery, communi- 

 cation is established between the arterial system and the manometer, 

 which now records the variations of arterial pressure. The tracing exhibits 

 larger (respiratory) undulations, on each of which many smaller undulations 

 (cardiac pulsations) are inscribed. It shows (i) that each contraction of the 



