PRACTICAL EXERCISES 187 



higher than that in the proximal limb by the amount needed to 

 exactly balance the pressure of the column of sodium carbonate in 

 the latter). Disconnect the arterial cannula from the manometer, 

 and allow the writing-point to trace a horizontal straight line (line of 

 zero pressure) on the drum (Figs. 56 and 57). 



20. The Influence of the Position of the Body on the Blood- 

 pressure. Inject into the rectum of a dog 3 to 4 grammes of 

 chloral hydrate dissolved in a little water. See that it does not run 

 out again immediately after injection. In ten minutes anaesthetize the 

 animal fully with the mixture of equal parts of alcohol, chloroform and 

 ether, known as the ACE mixture, or with chloroform, and tie it very 

 securely, back downward, on a board which can be rotated around a 

 horizontal axis, corresponding in position to the point at which the 

 cannula is to be inserted.* Set up a drum and manometer as in 19 

 (p. 185), but with a rubber connecting-tube of such length as will 

 allow free rotation of the board. Insert a cannula into the central 

 end of the carotid artery at a point immediately above the axis of 

 rotation of the board, and connect it with the manometer, (a) Take 

 a blood-pressure tracing with the board horizontal. () Whilst the 

 tracing is being taken, rotate the board so that the position of the 

 animal becomes vertical, with the feet down. Mark on the tracing 

 the moment when the change of position takes place. The pressure 

 falls. Replace the dog in the horizontal position. The manometer 

 regains its former level. Now rotate the board, till the animal is again 

 vertical, but with feet up and head down, and observe the effect on 

 the blood-pressure. The respiratory variations are greater with feet 

 down than with head down. Notice in both cases whether there is 

 any change in the rate of the heart. (<r) Take the board off the 

 stands, lay it on a table, expose the femoral artery, and insert a 

 cannula into it. Shift the axis so that it now lies below this cannula. 

 Replace the board on the stands, and repeat (a) and (b). The fall 

 of pressure will now take place in the head-down position.! 



21. Effects of Haemorrhage and Transfusion on the Blood- 

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

 cannula into the carotid artery, another into one femoral vein 

 (p. 177), and a third into the femoral artery on the opposite side. 



* A simple arrangement for this purpose is a board with a number of 

 staples fastened in pairs into its lower surface, so that an iron rod can be 

 pushed through any pair, and form a horizontal axis at right angles to 

 the length of the board. The dog having been tied down, the rod is 

 pushed through the pair of staples corresponding to the position of the 

 cannula in the artery that is to be connected with the manometer. The 

 projecting ends of the rod rest in two ordinary clamp-holders, fastened at 

 a convenient height on two strong stands, whose bases are clamped to the 

 end of a table. The other end of the board is supported by a piece of 

 wood that rests on the floor, and can be removed when the board is to be 

 rotated. 



t In 1 6 dogs the fall of pressure in the carotid in the feet-down 

 position varied from 12 to 100 mm. of mercury ; average fall, 44.4 mm, 

 In 12 out of the 16 animals the rise of pressure in the head-down position 

 varied from 2 to 36 mm. ; in I there was no change-; in 3 there was a fall 

 of 5 to 24 mm. 



