Chap. VII.] WOORARA EXPERIMENT. / 5 



K, then to the electro- magnets, and from there to 

 the brass support of A, and by the arm K to z, if the 

 bridge be lowered. When the electro-magnet acts and 

 attracts the keeper L, the contact between s t and the 

 platinum plate is broken and the current is interrupted. 

 The lever then, aided by its spring sp, flies back and 

 renews contact with s /5 and so the current is re-formed, 

 and immediately afterwards again broken by the 

 electro-magnets. By this means the little ivory 

 hammer h, when the apparatus is properly adjusted, is 

 kept beating on the nerve in the groove. The 

 attached limb is in consequence thrown into tetanus. 

 When the piece of nerve in the groove is beaten 

 through, a fresh piece is brought in by turning the 

 axle A. 



Bernard's woorara experiment is de- 

 signed to prove the Hallerian doctrine that irritability 

 is inherent in muscular tissue ; that is, that muscular 

 tissue can be made to contract by the direct application 

 of other than nervous stimuli. For this purpose a 

 drug obtained from South America, and called the 

 Indian arrow poison, woorara, curara, or urari, is used, 

 because it paralyses the terminations of the motor 

 nerves. Five grains of the crude drug are rubbed 

 up with a little weak spirit in a mortar, and five drops 

 of glycerine and three drachms of distilled water are 

 added. Of this solution, six minims (equal to about 

 g^-th of a grain) are injected by a hypodermic syringe 

 under the skin of a frog. In a short time the muscles, 

 first those of the limbs, then those of the trunk, become 

 paralysed, and the frog lies flat out. The frog is then 

 decapitated, and the usual nerve-muscle preparation 

 made, and fixed in a muscle telegraph. A nerve- 

 muscle preparation from an unpoisoned frog is next 

 made and fixed in another telegraph placed in line 

 with the first. The best arrangement is to have a 

 double telegraph, in which there is only one forceps for 



