448 



VETERINARY PHYSIOLOGY 



end of the manometer so that it nearly equals that in the 

 artery, and thus prevents the animal from bleeding into the 

 tube. 



With such an apparatus a record such as is shown in 

 fig. 188 is given. The actual pressure is measured by 

 taking the difference between the level of the mercury in 

 the two limbs of the tube. To make the measurement, it is 

 customary to describe an abscissa when the mercury is at 

 the same level in the two sides of the tube. The heisrht of 



Big. 189. — A., The Mercurial Manometer with Recording Float, used in 

 taking records of the arterial blood pressure of lower animals. The 

 clamped tube is to allow of the pressure being raised. The long tube 

 is connected with the cannula placed in the artery. B., The Riva 

 Rocci Sphygmometer, for measuring the arterial pressure in man. 

 M., manometer ; P., pump ; V., valve. 



the style above the abscissa must be multiplied by two to 

 give the pressure, on account of the depression in the 

 proximal limb which accompanies the rise in the distal 

 limb. 



On the record made with such an instrument, the 

 rhythmic variations in the arterial blood pressure already 

 considered on p. 434 et seq. are clearly visible (Practical 

 Physiology). 



