92 ELEMENTARY PHYSIOLOGY. XVII. 



Connect a receiving tambour (e.g. the "wrist tam- 

 bour" of Mackenzie's polygraph) with a recording tam- 

 bour by means of india-rubber tubing having a 3-way 

 glass tube on its course. The 3-way tube is for adjusting 

 the pressure, if necessary, in the recording tambour; the 

 latter should have a light lever about 6 inches long. 



The receiving tambour is placed on the wrist so that 

 the knob is on the cross mark on the skin, and before 

 fastening it, it is held steadily with varying pressure 

 and with slight variation of the position of the knob 

 and of the hand until the pressure and position which 

 give the maximum excursion of the lever of the record- 

 ing tambour is determined. It is then fastened on the 

 wrist. Arrange the lever to write on a revolving drum 

 and arrange the rate of the drum so that a single pulse 

 tracing takes about a centimetre. Whilst taking the 

 tracing the hand must be held perfectly still. 



Take a pulse tracing, note the quick primary rise 

 the systolic rise the gradual fall broken by the pre- 

 dicrotic and the dicrotic wave. In general the less the 

 peripheral resistance the quicker will be the primary 

 rise and fall and the greater the dicrotic wave, but the 

 curve is also affected by the force and frequency of the 

 heart-beat and by other factors. Note that slight varia- 

 tions in the position of the receiving tambour and in the 

 degree of flexion of the hand alter the pulse tracing. 



3. For the mercury manometer in 1 substitute one 

 having a float with writing point, and fix the mano- 

 meter near the drum so that its writing point is verti- 

 cally under that of the recording tambour ( 2). Re- 

 volve the drum to obtain a base line. Fasten the armlet 

 on the arm, and the receiving tambour on the wrist. 



