154 BLOOD PRESSURE. [BOOK i. 



corresponding to the heart beats, though the flow does not cease 

 between the jets. The blood is ejected with considerable force, 

 and may, in a large artery of a large animal, be spurted out to the 

 distance of some feet. The larger the artery and the nearer to the 

 heart, the greater the force with which the blood issues, and the 

 more marked the intermittence of the flow. The flow from the 

 distal cut end, that away from the heart, may be very slight, or 

 may take place with considerable force and marked intermittence, 

 according to the amount of collateral communication. 



When a corresponding vein is severed, the flow of blood, which 

 is chiefly from the distal cut end, that in connection with the 

 capillaries, is not jerked but continuous ; the blood comes out with 

 comparatively little force, and ' wells up ' rather than ' spurts out.' 

 The flow from the proximal cut end, that on the heart side, may 

 amount to nothing at all, or maybe slight, or may be considerable, 

 depending on the presence or absence of valves and the amount 

 of collateral communication. 



When an artery is ligatured, the vessel swells on the proximal 

 side, towards the heart, and the throbbing of the pulse may be 

 felt right up to the ligature. On the distal side, the vessel is 

 empty and shrunk, and no pulse can be felt in it unless there 

 be free collateral communication. 



When a vein is ligatured, the vessel swells on the distal side, 

 away from the heart, but no pulse is felt ; while on the proximal 

 side, towards the heart, it is empty and collapsed unless there be 

 too free collateral communication. 



96. When the interior of an artery, for instance the carotid, 

 is placed in communication with a long glass tube of not too great 

 a bore, held vertically, the blood, immediately upon the communi- 

 cation being effected, may be seen to rush into and to fill the tube 

 for a certain distance, forming in it a column of blood of a certain 

 height. The column rises not steadily but by leaps, each leap 

 corresponding to a heart beat, and each leap being less than its 

 predecessor; and this goes on, the increase in the height of the 

 column at each heart beat each time diminishing, until at last 

 the column ceases to rise, and remains for a while at a mean level, 

 above and below which it oscillates with slight excursions at each 

 heart beat. 



To introduce such a tube, an artery, say the carotid of a rabbit, 

 is laid bare, ligatured at a convenient spot, V Fig. 25, and further 

 temporarily closed a little distance lower down nearer the heart by a 

 small pair of ' bull-dog ' forceps, bd, or by a ligature which can be 

 easily slipped. A V-shaped cut is now made in the artery between 

 the forceps, bd, and the ligature /' (only the drop or two of blood 

 which happens to remain enclosed between the two being lost) : the 

 end of the tube, represented by c in the figure, is introduced into the 

 artery and secured by the ligature /. The interior of the tube is now 

 in free communication with the interior of the artery, but the latter 



