200 A MANUAL OF PHYSIOLOGY 



movements may occur, owing to anaemia of the medulla ob- 

 longata. 



25. Effects of Haemorrhage and Transfusion on the Blood- 

 pressure. Anaesthetize a dog with morphine and ether, and insert a 

 cannula into the trachea. Put a cannula into the central end of the 

 carotid artery and another into the central end of the femoral artery. 

 Then insert a cannula, which should have a piece of indiarubber 

 tubing 2 to 3 inches in length on its wide end, into the central end 

 of the femoral vein on the opposite side. In doing this more care 

 is necessary than 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) ligature, and cut one end short. 

 The piece of vein between it and the bulldog forceps is thus dis- 

 tended 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 o'g 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 of 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 22 (p. 195). Take the bulldog off the carotid, and 

 measure the difference in the level of the mercury in the two limbs 

 of the manometer 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. 



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

 100 c.c.* of 0-9 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. 



* 200 c.c. for a large dog. 



