212 THE CIRCULATION OF THE BLOOD AND LYMPH 



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 23 (p. 208), 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 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 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 position. 

 If the chloroform anaesthesia is light the reflex may not be abolished 

 in the feet-down position, although strong respiratory movements may 

 occur, owing to anaemia of the medulla oblongata. 



26. 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 



* 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 re- 

 moved when the board is to be rotated. 



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

 varied from 12 tp 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. 



