470 ON THE PHYSIOLOGICAL ACTION OF CASCA BAlllv. 



were left intact. After injecting a dose of casca the vessels 

 in both ears became pale, and apparent 'y there was no differ- 

 ence between them in the ear with the divided nerve and in 

 the other. 



We are rather inclined to the supposition that it does act on 

 some such centre or centres — possibly ganglia — in or around 

 the vessels themselves, because the local application of casca to 

 a frog's foot, or its injection under the skin of the back, causes 

 no contraction in the vessels of the web, as one would expect it 

 to do if it acted on the vessels themselves. The arterioles begin 

 to contract after a small dose of casca before any effect is 

 produced on the vagus, so that the blood-pressure begins to rise 

 before the pulse becomes slow. The contraction also seems to 

 last after the vagus is paralysed, and even after the heart has 

 ceased to beat, so that when the animal is dying the blood- 

 ^iressure falls very slowly. 



The contraction of the vessels after the injection of casca is 

 mot confined to those which are under the dominion of the vaso- 

 motor centre in the medulla. It has been shown by Ludwig 

 -and Hafiz that while this centre can cause contraction of the 

 vessels going to the intestines, it has little or no power over 

 those supplying the muscles. Thus it happens that when this 

 • centre is irritated the blood-pressure does not remain high 

 •during the cardiac diastole, as one formerly supposed it would 

 do; for although the intestinal arterioles are firmly contracted, 

 and prevent any blood from flowing into the veins, the arteries 

 •of the muscles remain uncontracted and the blood flows rapidly 

 through them. As the blood-pressure after the injection of 

 •casca remains so high during the cardiac diastole, the arterioles 

 in the muscles must be contracted as well as those in the 

 intestines. In its mode of action upon the blood-vessels casca 

 -differs from digitalis, but agrees with ergot, wdiicli seems to 

 cause contraction by acting rather upon peripheral vaso-motor 

 nerves or ganglia, or on the muscular wall of the blood-vessels, 

 than on the vaso-motor centre. 



Action on the Kidneys. — As the action of casca on the circula- 

 tion so closely resembles that of digitalis, it seemed not 

 improbable that it might also have a diuretic action, and we 



