7o 



A MANUALOF VETERINARY PHYSIOLOGY 



Effect of Gravity on Blood-Pressure. — L. Hill has demonstrated 

 the influence on the blood-pressure of hydrostatic pressure due 

 to gravity. He has shown in man that the arterial pressure is 

 higher in the erect than in the horizontal position ; that it is 

 higher in the leg than in the arm to the extent of the column 

 of blood separating the two points of measurement. Whether the 



Fig. 28. — Arrangements for taking a Blood-Pressure Tracing (Stewart). 



M, Manometer ; Hg, mercury ; F, float armed with writing-point ; A, thread 

 attached to a wire projecting from the drum, and supporting a small weight. 

 The thread keeps the writing-point in contact with the smoked paper and 

 the drum. B is a strong rubber tube connecting the manometer with the 

 artery ; C a pinch -cock on the rubber tube, which is taken off when a tracing 

 is to be obtained. 



body is placed in the horizontal, vertical, or inverted position, 

 the blood-pressure in those arteries at the same level as the 

 heart remains little altered, but in the vessels below the heart 

 the pressure is increased. Constant compensations are occurring 

 in the circulatory system to guard against important alterations 

 in blood-pressure due to gravity. These are effected by a 

 variable output of blood from the heart, but especially by dila- 



