294 



MANUAL OF PHYSIOLOGY. 



The modern accurate methods of research have taught us the 

 differences in pressure that exist in the various parts of the vascu- 

 lar system. However, direct measurement can only be accom- 

 plished in vessels of such a size as to admit a canuula, hence the 

 pressure in the capillaries, in the very minute arteries and veins 

 can only indirectly be estimated. The pressure in all parts of 

 the vascular system is subject to frequent variation to be presently 



FIG. 134. 



Diagram showing the relative height of the blood pressure in the difU-ivnt 

 regions of the vessels. H. Heart. A. Arteries, a. Arterioles. c. Capil- 

 laries, v. Small veins, v. Large veins. H. v. being the zero line, the pres- 

 sure is indicated by the elevation of the curve. The numbers on the left 

 give the pressure (approximately) in mm. of mercury. 



mentioned, but this table may be useful in giving a general idea 

 of the average permanent differences that exist in the different 

 vessels of large animals and man. 



Lurge arteries (Carotid, Horse) -f- 160 mm., mercury. 

 Medium " (Brachial, Man) -f 120 mm., " 

 Capillaries of Finger, -f~ 38 mm., " 



Small Veins of Arm, -j- 9mm., " 



Large Vein of Neck, 1 to 3 mm., " 



