126 



PRACTICAL PHYSIOLOGY 



which has a small air-chamber above. Near the open end is a side 

 hole- the zero of the scale. On placing the open end in water, a 

 meniscus rises to the side hole. 



A short length of rubber tubing, attached to a rubber bag, is slipped 

 over the open end so as to cover the side hole. The bag is half 

 distended with air, and is enclosed in a silk cover. The bag being 

 enclosed by the palm of the hand, and the gauge held erect between 



FIG. 126. Effect of abdominal and chest breathing. (Lewis. ) 



the fingers, the bag is pressed down upon the radial artery of the 

 subject, the thumb exerting counter pressure against the back of the 

 wrist. The index finger of the other hand feels when the pulse is 

 obliterated, while the second finger prevents, if necessary, the pulse 

 getting through from the anastomoses with the ulnar artery. The 

 water used for the meniscus is made alkaline with potash to avoid the 

 effect of grease in the tube. If the meniscus does not rise to the side 

 hole, blow through this and try again. 



The air-chamber acts as a spring, and the instrument is a spring 

 manometer. The meniscus is set before each reading, so as to avoid 

 errors due to alterations of temperature and barometric pressure. The 



