468 ON THE PHYSIOLOGICAL ACTION OF CASCA BARK. 



tractecl before finally stopping, the lower part of tlie ventricle 

 in one experiment having been contracted, while the upper half 

 was not, so that the lower half appeared to be partly pushed up 

 into the upper in such a way as to produce a deep transverse 

 wrinkle across the middle of the ventricle. 



Action on the Vagus. — It will be seen from the description 

 thus given that the action of casca upon the heart of the frog 

 is almost exactly like that of digitalis, as described by Messrs. 

 Fagge and Stevenson.* Further experiments have shown us 

 that casca also resembles digitalis in its action upon the vagus. 

 A moderate dose of casca injected into the jugular vein first 

 slows the heart, a further dose greatly quickens it, and another 

 large dose again slows it. Tlie first slowing is due to stimula- 

 tion of the vagus roots in the medulla oblongata, for when the 

 vagi are divided so as to cut the communication between the 

 medulla and the heart, the pulsations again become quick. The 

 quickening which a large dose of casca produces when the vagi 

 are uninjured is due to its paralysing the ends of these nerves 

 in the heart, and thus destroying the communication between 

 this organ and the medulla quite as effectually as the division 

 of their trunks by the knife. When the nerves, as they pass 

 down the neck, are irritated by an induced galvanic current in 

 their normal condition, they slow the pulsations of the heart, or 

 stop it altogether; but after the injection of casca has paralysed 

 their ends in the heart, no irritation of their trunks has any 

 power to slow its pulsations. The final slowing produced by a 

 large dose of casca must be due to the action of the drug upon 

 the ganglionic apparatus within the heart itself, as the vagus 

 ends are already paralysed. The extreme slowness of the heart 

 in this stage is sometimes very remarkable, as in one experiment 

 there were only three pulsations per minute, only one occurring 

 in the time occupied by three or four respirations. 



Action on the Blood-vessels. — Casca has a most extraordinary 

 power of contracting the blood-vessels. This is indicated b\ 

 the pressure of blood within the vessels becoming high after its 

 inj(iction, notwithstanding the slowness of the heart's action ; 

 but it is proved most unmistakably by the fact that during the 



* Proceeditijs of the Royal Socie'7/, vol. xiv, p. 270. 



