MAREY'S SPHYGMOGRAPH. 233 



These movements, sometimes called the " cardio-pneumatic 

 movements," are due to the variations of the size of the heart 

 during its several phases of fulness, altering the volume of air 

 in the lungs. 



5. Reflex Inhibition of the Heart. 



(a.) Place one hand over the chest of a rabbit and feel 

 the beating of the heart. With the other hand suddenly 

 close the nostrils of the rabbit, or bring a little ammonia 

 near the nostrils, so as to cause the animal to close them. 

 Almost at once the heart can be felt to cease beating for a 

 time, but it goes on again. 



6. Effect of Swallowing. 



(a.) With your watch in front of you, count the number 

 of your own pulse-beats per minute, and then slowly sip 

 a glass of water, still keeping your finger on your pulse. 

 Count the increase in the number of pulse-beats during the 

 successive acts of swallowing. This is due to the inhibitory 

 action of the vagus being set aside. 



LESSON LIU. 



THE PULSE SPHYGMOGRAPHS SPHYG- 

 MOSCOPE PLETHYSMOGRAPH. 



1. The Pulse. 



(a.) Feel the pulse of a fellow-student, count the number 

 of beats per minute ; compare its characters with your own 

 pulse, including its volume and compressibility. Observe 

 how its characters and frequency are altered by exercise and 

 by a prolonged and sustained deep inspiration. 



2. The Sphygmograph. Many forms of this instrument are 

 in use. Study the forms of Marey and Dudgeon. 



Marey's Sphygmograph (Fig. 108). 



