1NNEKVA11ON Of HEART AND BLOOU-VESSELS 5 , u 



This experiment requires much care and close 

 observation. The curare effect must be very 

 slight; a small quantity of the drug should be 

 given an hour before the observation is made. 

 Great pains must be taken to use feeble currents 

 and not to prolong the excitation, for the vaso- 

 motor nerves are rapidly exhausted. The nar- 

 rowing of the arteries of the web is usually 

 evident only in the slowing of the blood-stream 

 during excitation. 



Vasodilator Nerves. 1. Kepeat the preceding 

 experiment in a frog in which the sciatic nerve has 

 been four days severed (without injury to the fem- 

 oral vessels). On stimulation of the peripheral 

 segment of the divided sciatic nerve, the vessels 

 of the web will dilate instead of constricting. 



Evidently the sciatic nerve contains vasodilator 

 as well as vasoconstrictor fibres. When the 

 sciatic fibres are separated from their cells of 

 origin by the section of the nerve, the fibres distal 

 to the section degenerate. But the degeneration 

 does not proceed at the same rate in all the fibres. 

 The vasoconstrictors die before the vasodilators. 

 In ordinary stimulation of the normal nerve, the 

 action of the constrictors overpowers that of the 

 dilators. In the partially degenerated nerve, 

 the same stimulation causes dilatation because 

 the constrictor fibres are dead or dying. 



