CIRCULATION OF THE BLOOD. 



527 



carotid arteries is then raised on a blunt hook, the connective tissue gently torn 

 away -with two pairs of forceps, and the artery freed from the surrounding nerves 

 and fibrous tissue. After the blood-vessel is so isolated for a distance of about 

 an inch, it is firmly ligated at the extremity of the free portion nearest to the 

 head, and a thread is then tied in a loop-knot around the artery at the end of its 

 freed extremity nearest to the heart. A small cut is then made in the interme- 

 diate portion with a pair of scissors, and a slightly constricted glass tube inserted 

 into the interior of the artery and bound fast with a thread. This glass tube is 

 then to be filled by a pipette with a saturated solution of sodium bicarbonate, to 

 pre vent coagulation of the blood, and the cannula then connected by thick rubber 

 tubing, also filled with the same solution, with the proximal arm of the manome- 

 ter. Care should be taken that all air-bubbles are removed from the cannula, 

 rubber tube, and proximal arm of the manometer, so that the entire tubing, from 

 the level of the mercury to the interior of the carotid, is completely filled with 

 soda solution. If, now, the slip-knot previously tied around the carotid is 



Fig. 218.— Mercurial Manometer for Measuring and Recording the 

 Blood Pressure. (Yeo.) 



«, proximate limb of the manometer ; 6, union of the two limbs of the manometer ; e, the rod floating 

 in the mercury carries the writing point; d, stop-cock through which the sodium bicarbonate can be 

 introduced between the blood and the mercury of the manometer. 



loosened, thus establishing communication between the interior of the artery and 

 the manometer, the blood at once rushes from the artery into the connecting tube, 

 and so causes the level of mercury to be depressed in the proximal arm and rise 

 in the distal arm. This rise of mercury occurs very rapidly, in jerks correspond- 

 ing to the beats of the heart, and soon reaches its maximum. When this point is 

 attained, the mercury does not remain level, but undergoes rapid oscillations, 

 each rise corresponding to the systole of the ventricle, each fall correspond- 

 ing to the diastole. If a float, swimming on the top of the mercury, in the 

 distal arm of the manometer be allowed to record its up-and-down movements 

 on a moving surface, as, for example, the revolving drum of the kymographion 

 (Fig. 219), a series of curves will be produced, in which each ascent cor- 

 responds to the contraction of the ventricle, each descent to its diastole (Fig. 

 220). In the experiment, as above described, it is evident that a considerable 

 quantity of blood will leave the arterial system and fill the tube of the manometer. 



