PRACTICAL EXERCISES 199 



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

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

 hydrate dissolved in a little water. See that it doss not run out 

 again immediately after injection. In ten minutes anaesthetize the 

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

 ether (one of the so-called A.C.E. mixtures), 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 22 (p. 195), but with a rubber connecting-tube of such length 

 as will allow free rotation of the board. Put a cannula in the 

 trachea. 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. 



(b) 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 hori- 

 zontal 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 in the pressure are usually greater with 

 feet down than with head down. Notice in both cases whether 

 there is any change in the rate of the heart. 



(c) 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. f In the feet-down position 

 (with the cannula in the femoral artery) a rise of pressure in 

 general takes place. But sometimes this is very small, and lasts 

 only a few seconds, being succeeded by a fall, during which the 

 heart-beats on the tracing are much weaker than before, since 

 enough blood is not reaching the heart to enable it to maintain 

 the pressure. In the feet-down position see whether the corneal 

 reflex can be got. If not, as is likely, turn the animal into the 

 head-down position. The reflex may now soon be obtained, and 

 it may again disappear on putting the animal in the feet-down 



Eosition. If the chloroform anaesthesia is light the reflex may not 

 e abolished in the feet-down position, although strong respiratory 



* 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. 



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

 tion varied from 12 to 100 mm. of mercury ; average fall, 44*4 mm. In 

 12 out of the 1 6 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. 



