1*4 



A MANUAL OF PHYSIOLOGY 



into the tambour, and it is well to insert a piece of glass tubing in the 

 connection between it and the plethysmograph, so that it may be seen 

 when the water is rising too high. Adjust a time-marker to write 

 half or quarter seconds (Fig. 60, p. 170). Mosso's plethysmograph 

 (Fig. 72) may also be used. 



(1) Take tracings with arm (a) horizontal, (b) hanging down. 



(2) With the arm horizontal, take tracings to show the effect (a) of 

 closing and opening the fist inside the plethysmograph ;* (fr) of apply- 

 ing a tight bandage round the arm a little way above the indiarubber 

 band ; (c) of inhaling 2 drops of amyl nitrite. 



1 8. Pulse-rate. (i) Count the 

 radial pulse for a minute in the 

 sitting, supine, and standing posi- 

 tions. Use a stop-watch, setting 

 it off on a pulse-beat and counting 

 the next beat as one. Make three 

 observations in each position. 



(2) Count the pulse in a person 

 sitting at rest, and then again in 

 the sitting position immediately 



FIG. 72. PLETHYSMOGRAPH (Mosso). 



M, balanced test-tube, in communication with Z). When water passes from vessel 

 D to M, or from M to D, M moves down or up, and its movements are recorded by 

 the writing-point N. M is steadied by the liquid in P, into which it dips. 



after active muscular exertion. Note how long it takes before the 

 pulse-rate comes back to normal. 



(3) Count the pulse in a person sitting at rest. Repeat the obser- 

 vation while water is being slowly sipped, and note any change. 



(4) With one hand over the thorax of a rabbit, count its pulse. 

 Then notice the effect (a) of suddenly closing its nostrils, (b) of 

 bringing a small piece of cotton-wool sprinkled with ammonia 01 

 chloroform in front of the nose (reflex inhibition of the heart). 



* Closing the fist causes a fall in the curve, i.e., a diminution in the 

 volume of the arm. On opening the hand, the curve regains its level. 



