208 BLOOD PRESSURE. [BOOK i. 



FIG. 26. APPARATUS FOR INVESTIGATING BLOOD PRESSURE. 



At the upper right-hand corner is seen, on an enlarged scale, the carotid artery, 

 clamped by the forceps bd, with the vagus nerve v lying by its side. The artery 

 has been ligatured at V and the glass cannula c has been introduced into the artery 

 between the ligature I' and the forceps bd, and secured in position by the ligature I. 

 The shrunken artery on the distal side of the cannula is seen at ca'. 



p.b. is a box containing a bottle holding a saturated solution of sodium car- 

 bonate or of sodium bicarbonate or a mixture of the two, and capable of being 

 raised or lowered at pleasure. The solution flows by the tube p.t. regulated by the 

 clamp c" into the tube t. A syringe, with a stopcock, may be substituted for the 

 bottle, and attached at c". This indeed is in many respects a more convenient plan. 

 The tube t is connected with the leaden tube t, and the stopcock c with the mano- 

 meter, of which m is the descending and in' the ascending limb, and s the support. 

 The mercury in the ascending limb bears on its surface the float fl, a long rod 

 attached to which is fitted with the pen p, writing on the recording surface r. The 

 clamp cl. at the end of the tube t has an arrangement shewn on a larger scale 

 at the right-hand upper corner. 



The descending tube m of the manometer and the tube t being completely filled 

 along its whole length with fluid to the exclusion of all air, the cannula c is filled 

 with fluid, slipped into the open end of the thick- walled indiarubber tube t, until it 

 meets the tube t (whose position within the indiarubber tube is shewn by the dotted 

 lines), and is then securely fixed in this position by the clamp cl. 



The stopcocks c and c" are now opened, and the pressure-bottle raised or fluid 

 driven in by the syringe until the mercury in the manometer is raised to the 

 required height. The clamp c" is then closed and the forceps bd removed from the 

 artery. The pressure of the blood in the carotid ca. is in consequence brought to 

 bear through t upon the mercury in the manometer. 



If a float, swimming on the top of the mercury in the ascending 

 limb of the manometer, and bearing a brush or other marker, be 

 brought to bear on a travelling surface, some such tracing as that 

 represented in Fig. 27 will be described. Each of the smaller 



FIG. 27. TRACING OF ARTERIAL PRESSURE WITH A MERCURY MANOMETER. 



The smaller curves p p are the pulse-curves. The space from r to r embraces 

 a respiratory undulation. The tracing is taken from a dog, and the irregularities 

 visible in it are those frequently met with in this animal. 



curves (p, p) corresponds to a heart beat, the rise corresponding to 

 the systole and the fall to the diastole of the ventricle. The larger 

 undulations (r, r) in the tracing, which are respiratory in origin, 

 will be discussed hereafter. In Fig. 28 are given two tracings 

 taken from the carotid of a rabbit ; in the lower curve the record- 

 ing surface is travelling more rapidly than in the upper curve; 

 otherwise the curves are alike and repeat the general features of 

 the curve from the dog. 



