NERVUS SPLANCHNICUS AND ADRENALS 45 



together and fasten them by a cHp, to protect the underlying tissues from 

 drying. 



Return to the carotid artery. Bring the right forelimb into a posture of 

 extension, leaving it retracted alongside the chest by means of a hook-weight 

 attached to the paw. See that the arterial tube from the manometer easily 

 reaches the exposed artery. The pressure provided in the manometer should 

 be about 70 mm. Hg. Choose a cannula and insert it into the artery, making 

 the connexions with manometer as in previous exercises. 



VII. Open the loin wound carefully. When the kymograph record has 

 been running satisfactorily for half a minute or so, place the secondary coil at 

 13 cm., close the primary circuit, and start the magnetic interrupter. Holding 

 up the splanchnic nerve by the ligature, apply to it the needle electrodes, 

 setting them cross- wise on the nerve and seeing that they are not in contact 

 with any other part or tissue. Then un-short-circuit the electrodes (shunt 

 key in secondary circuit) and stimulate. 



An increase of blood-pressure ensues almost immediately. To obtain 

 full effect a stimulation period of about 5" may be required. The rise occurs 

 in two steps ; the earlier of these is due to direct action of the vasoconstrictor 

 nerve-fibres on the muscular coat of the arteries and arterioles ; the slight 

 fall which almost invariably breaks the ascent of the curve is to be regarded 

 as caused by discharge from the adrenal medulla of a small amount of 

 adrenaline, whose action contributes also to the subsequent reascent and heart 

 acceleration. Secretory fibres to the adrenal medulla are contained in the 

 splanchnic nerve. A very small dose of adrenalin causes in the cat a slight 

 transient fall of arterial pressure, though a larger dose produces a rise (Cannon 

 and Nice, Amer. Jnl. of Physiol 1913, vol. xxxii, p. 44). Note the quickening 

 of heart-rate in the second rise. 



VIII. Pass a ligature round r. adrenal vessels : the gland is almost Obs. 29. 

 sessile on the inferior vena cava. Leave the Hgature loose but ready to tie. '^^^ adrenal 



Stimulate the splanchnic nerve again, recording the effect with the splan chnic 

 kymograph. Then draw tight the noose round the right adrenal vein, reaction. 

 Repeat the stimulation, recording the result. The rise in arterial pressure is 

 now usually a simple one without the two successive steps it showed 

 previously. Remove right adrenal altogether : repeat stimulation as before. 



[IX. Deepening the splanchnic wound with the fingers and the scalpel Obs. 30. 

 handle, carefully pass across the inferior vena cava, already exposed, and the ^^P^^^i* °^ 

 abdommal aorta towards the left side of the preparation. The left splanchnic after section 

 nerve is then at once met with. Sever it. Readjust the wound and cover it. of both n. 



splanchnici. 



