750 DR FRASER ON THE PHYSIOLOGICAL ACTION 



1 hour 50 min. afterwards, 



/ galvanism of the left vagus produced stoppage of all the 



) chambers ; and the heart remained at rest, in diastole, *for 

 1 ten minutes, when a feeble auricular contraction occurred, 



v and, soon after, a ventricular, 

 r r ( galvanism of either sciatic nerve caused merely faint twitches of 



( the toes. 



( cardiac contractions = 18 per minute ; very feeble, but rhyth- 



I mical. 



( strong and continued galvanism of the left vagus produced no 



( effect on the cardiac contractions. 



C strong and continued galvanism of the right vagus, which had 

 2 ,. 18 ., ■< not been irritated during the experiment, produced no effect 



\ on the cardiac contractions. 

 2 ,, 20 ., strong galvanism applied to either sciatic nerve produced no effect, 



f cardiac contractions stopped. Irritation could produce a few 



1 contractions for only a few minutes longer. 



10 

 15 



2 ., 40 



From this experiment it is apparent that the vagi retain their inhibitory power 

 over the heart during the whole period that its action is being modified by 

 physostigma. Ultimately, however, they are themselves paralysed, as might be 

 anticipated from the analogies that exist between them and the spinal nerves ; and, 

 as this and many other similar experiments prove, the functions of the vagi and 

 of the spinal motor nerves are lost simultaneously, or nearly so. 



To illustrate this in warm-blooded animals, it is necessary to exhibit so small 

 a dose of the poison that death shall be caused by asphyxia, and the heart 

 afterwards continue to contract, however irregularly. 



Experiment LI I. 



Half a grain of extract, suspended in ten minims of distilled water, was injected under the 

 skin on the back of a full-grown and active rabbit. The usual symptoms followed; and, in thirty- 

 four minutes, the animal was dead, all respiratory movement having ceased. Immediately after 

 wards, the heart was exposed ; and it was found contracting in normal rhythm, twenty-two times 

 in the minute. The right vagus was divided ; and the end proximal to the heart was galvanised, 

 with the effect of producing an immediate stoppage, in diastole, for several seconds. The vagi were 

 tested, occasionally, during twenty minutes after the rabbit's death, and their cardiac inhibitory 

 function, as well as their excito-motory power over the stomach and oesophagus, continued 

 active all this time ; and, for the same period, the sciatic, intercostal, phrenic and other spinal 

 nerves retained their motor conductivity. Twenty-two minutes after death, the heart was con- 

 tracting eight times per minute. Galvanism of either vagus could now neither stop the cardiac 

 action nor excite oesophageal or gastric movements. The sciatic and other spinal nerves were 

 tested at twenty-five minutes after death, and found to be perfectly paralysed. 



It is, therefore, quite possible, as far, at least, as conveyance by the vagi 

 nerves is concerned, for Calabar bean to act on the heart by exciting the cardiac 

 inhibitory centre in the medulla oblongata. But, if this be the method of its 

 action, the prevention of this possible influence, by division or previous paralysis 

 of the vagi, or by destruction of the medulla oblongata, should render it impos- 

 sible for Calabar bean to produce its usual effects on the heart. 



