PRACTICAL EXERCISES 211 



size of the float properly adjusted to that of the tube, this is not neces- 

 sary, and is to be avoided. Then, tilting the tube carefully, fill the 

 proximal limb (i.e., the limb which is to be connected with the blood- 

 vessel) with a saturated solution of sodium carbonate or a half -saturated 

 solution of magnesium sulphate, or, what is better for most purposes, 

 a 2 per cent, solution of sodium citrate. This is easily done by means 

 of a pipette furnished with a long point. Now attach a strong rubber 

 tube to the proximal end of the manometer, and fill it also with the 

 solution. All air must be got out of the manometer and its connecting- 

 tube. Raise the end of the rubber tube and blow into it, so as to cause 

 a difference of about 10 cm. in the height of the mercury in the two 

 limbs of the manometer, and, without releasing the pressure, clamp the 

 tube with a pinchcock or screw clamp (Fig. 4 - , p. no). 



Now smoke a drum, and arrange the writing-point of the manometer- 

 float so that it will write on it. Suspend a small weight by a piece of 

 silk thread from a support attached to the stand of the drum, so that 

 it hangs down outside of the writing-point of the manometer-float and 

 always keeps it in contact with the smoked surface without undue 

 friction. Or a piece of glass rod drawn out to a fine thread in the 

 blowpipe flame answers very well. Below the writing-point of the 

 float, and in the same vertical line with it, adjust the writing-point 

 of a time-marker beating seconds (Fig. 88, p. 195). 



Next fasten the animal on a holder, back down. Give ether and 

 insert a tracheal cannula (p. 202). (The tracheal cannula is not abso- 

 lutely required for the experiment, but it is convenient, as the animal 

 is more under control, and artificial respiration can be begun at any 

 moment, should this be necessary.) Insert a glass cannula, armed 

 with a short piece of rubber tubing, into the central (cardiac) end of 

 the carotid artery (p. 63). Leaving the bulldog forceps on the artery, 

 fill the cannula and tube with the sodium citrate or one of the other 

 solutions. Slip the rubber tube over a short glass connecting-tube. Fill 

 this also with the solution, and connect it with the manometer-tube, 

 seeing that both are quite full of liquid, so that no air may be enclosed. 



Where a permanent working place is provided for blood-pressure 

 experiments it is convenient to connect the cannula and manometer 

 with a pressure -bottle containing the sodium citrate solution, and to 

 use a three-way cannula for the bloodvessels (Fig. 103). The cannula 

 has a bulbous enlargement, which hinders clotting. The end of the 

 cannula is connected with the tube from the pressure -bottle, which is 

 closed by a clip, and the side-tube is connected with one limb, E, of 

 the manometer shown in Fig. 104. E is itself provided with a side- 

 tube, F, armed with a short piece of rubber tubing. The cannula does 

 not require to be filled with liquid before being inserted into the artery. 

 By opening F and releasing the clip on the tube from the pressure- 

 bottle the cannula and the tube connecting it with the manometer can 

 be filled, and any blood-clots can be easily washed out in the course of 

 an experiment. Before the bulldog forceps is taken off the artery to 

 obtain a blood-pressure tracing, F must be closed, and the clip on the 

 tube from the pressure-bottle opened. The bottle is attached to a 

 strong cord passing over a pulley, by which it is raised to a height 

 sufficient to balance approximately the pressure in the artery. The 

 tube to the pressure-bottle is then clipped. If no manometer with 

 side-tube is available, a T-piece can be inserted in the connection 

 between the cannula and the manometer, and the cannula can be 

 washed out through this. 



Now take the bulldog forceps off the artery, and allow the drum to 

 revolve at slow speed. The writing-point of the manometer-float will 



