PRACTICAL EXERCISES 213 



in putting a cannula into an artery. Feel for the femoral artery, cut 

 down over it, and with forceps or a blunt needle separate the femoral 

 vein from it for about an inch. Pass two ligatures under the vein, and 

 tie a loose loop on each. Put a pair of bulldog forceps on the vein 

 between the ligatures and the heart. Now tie the lower (distal) liga- 

 ture, and cut one end short. The piece of vein between it and the 

 bulldog forceps is thus distended with blood, and this facilitates the 

 next step. With fine-pointed scissors make a snip in the wall of the,, 

 vein. The cannula is now pushed through the slit in the vein, and 

 the upper ligature tied firmly round its neck. By the aid of a pipette, 

 made by drawing a piece of glass tubing out to a long point, the cannula 

 and rubber tube are then completely filled with 0*9 per cent, salt 

 solution. Be sure to pass the point of the pipette right down to the 

 point of the cannula, so as to dislodge any bubble ol air that may tend 

 to cling there. Then, holding up the open end of the rubber tube, 

 close it, without allowing any air to enter, by means of a screw clamp 

 or bulldog forceps, or a small piece of glass rod. Connect the cannula 

 in the carotid with a manometer, arranged to write on a drum as in 

 experiment 23 (p. 208). Take the bulldog off the carotid, and measure 

 the difference in the level of the mercury in the two limbs of the man- 

 ometer with a millimetre scale. 



(1) (a] While a tracing is being taken, draw off about 10 c.c. of blood 

 from the femoral artery, and observe whether there is any effect on 

 the tracing. Mark on the tracing the moment when the removal of 

 the blood begins and ends. 



(b) Repeat (a), but run off about 100 c.c.* of blood, and let this be 

 immediately defibrinated. Then draw off portions of 100 c.c.* at short 

 intervals until a distinct fall of blood-pressure has been produced. All 

 the samples of blood should be defibrinated and strained through 

 cheese-cloth. 



(2) (a) Now, while a tracing is being taken, inject the whole of the 

 defibrinated blood slowly through the cannula in the femoral vein by 

 means of a funnel supported by a stand at such a height that the blood 

 runs in easily. A pinchcock should be put on the tube connecting the 

 funnel and the cannula, and this should be closed before the funnel is 

 quite empty, so as to obviate any risk of air getting into the vein. Of 

 course, the cannula and connecting-tubes must all be freed from air 

 before injection is begun. Again measure the difference in the level 

 of the mercury and compare the pressure with that observed before 

 the first haemorrhage. 



(6) Inject into the vein, while a tracing is being obtained, about 

 100 c.c.* of o - 9 per cent, salt solution heated to 40 C., and go on 

 injecting portions of 100 c.c. until a distinct rise of pressure has taken 

 place, keeping a record of the total amount injected, and marking the 

 time of each injection on the curve. 



(c) After an interval of thirty minutes, again measure the height of 

 the mercury in the manometer. Then bleed the dog to death while a 

 tracing is being recorded. 



27. The Influence of Proteoses (and Peptones) on the Blood-Pressure. 

 Set up the apparatus for taking a blood-pressure tracing as in experi- 

 ment 23 (p. 208), but omit the induction-coil. Weigh a dog. Weigh 

 out a quantity of Witte's peptone equivalent to 0*5 grm. for every kilo 

 of body-weight. Dissolve the peptone in about ten times its weight 

 of o - 9 per cent, salt solution. Anaesthetize the dog with morphine and 

 ether or A.C.E. mixture. Insert a cannula into the trachea. Put 

 cannulae into the central end of one carotid and of one femoral vein 



* 200 c.c. for a large dog. 



