466 ON THE PHYSIOLOGICAL ACTION OF CASCA BARK. 



the s2-)inal cord or enceplialon. Thus loss of muscular power 

 may be due to loss of power eitlier in the muscles themselves — 

 in the motor nerves which supply them — or in the nerve-centres 

 in the spinal cord or encephalon. 



Action on 3fusdes.^T\ns was tested by laying one gastro- 

 cnemius of a frog in a solution of casca, and the other in an 

 indifferent liquid, such as a "75 per cent, solution of common 

 salt. After some time the excitability of the two muscles by 

 electrical stimuli was compared, and also their power to lift 

 weights. They were found to be equal. This showed that 

 casca was not a muscular poison, for liad it been so, the muscle 

 immersed in a solution of it would have lost its excitability 

 before the other, and its power to lift a weight would have 

 been lessened. 



Action on Motor Nerves. — In order to ascertain whether the 

 motor nerves were paralysed or not, the artery going to one 

 leg of a frog was ligatured and the poison injected under the 

 skin of the back. The poison was thus carried to every part 

 of the frog except the ligatured leg. Immediately after death 

 the excitability of the motor nerves Avas tested by the appli- 

 cation of an induced electrical current from a Du Bois Eey- 

 mond's coil. It was found that the motor nerves of the leg to 

 which the poison had been carried by the blood were not para- 

 lysed, and were quite as easily excited as those of the other 

 leg from which the poison had been excluded by ligature of tlie 

 artery. The poison, therefore, does not paralyse the motor 

 nerves. 



Action on the Spinal Cord. — Some time after the injection 

 of casca under the skin of a frocj the movements of the 

 animal become more sluggish, are imperfectly performed ; 

 and when the toes are pinched, the foot is either moved lazily 

 or not at all, instead of being promptly drawn up, as it 

 normally is. The reflex activity of the cord is thus seen to 

 be impaired, but we must not hastily conclude that this impair- 

 ment is due to the direct action of the drug upon the nervous 

 structures ; for imperfect circulation of blood through the brain 

 and spinal cord quickly deprives them of their power, and 

 although stoppage of the circulation does not abolish the 



