26 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



time shows, first, that the muscle protoplasm can be irritated directly, and 

 secondly, that the nerves do not communicate directly with the muscles, but 

 stimulate them through the agency of terminal end-organs, called motor end- 

 j id itcs? 



Qurare Experiment. — Rapidly destroy the brain of a frog with a slightly 

 curved, blunt needle, and, to prevent hemorrhage, plug the wound by thrust- 

 ing a pointed match through the foramen magnum into the brain-cavity. 

 Expose the sciatic nerve of the left thigh, carefully pass a ligature under it, and 

 tie the ligature tightly about all the tissues of the thigh excepting the nerve, 

 thus cutting off the circulation from all the leg below the ligature without in- 

 jury to the nerve. Inject into the dorsal lymph-sac or the abdominal cavity a 

 f< \v drops of a 2 per cent, solution of curare. In from twenty to forty minutes 

 the drug will have reached the general circulation and produced its effect. 



Although the brain has been destroyed and the frog is incapable of having 

 sensation, it will be found that muscular movements will be made if the skin 

 be pinched soon after the drug has been given. These are reflex movements, 

 and are due to excitation of the spinal cord by the nerves connected with the 

 skin. As the paralyzing action of the drug progresses, these reflex actions be- 

 come feebler and feebler until altogether lost in the parts exposed to the drug, 

 although they may still be shown by the parts from which the drug has been 

 excluded. The condition of the nerves and muscles can be examined as soon 

 as reflex movements of the poisoned parts cease. 



To ascertain the action of the poison, expose the nerves of the two legs, 

 either high up in the thigh or inside the abdominal cavity, where they have 

 been subjected to the poison, and test their irritability by exciting them with 

 electric shocks. Stimulation of the motor nerve of the right leg («, Fig. 4) 

 causes no contraction of the muscles of that leg, while stimulation of the motor 

 nerve of the left leg (b), results in active movements of the muscles of that 

 leg. The response of the left leg shows that nerve-trunks are not injured by 

 the poison, and that the paralysis of the right leg must Hud some other expla- 

 nation. On testing the muscles it is found that they are irritable and contract 

 when directly stimulated. Since neither nerve-trunks nor muscles are poisoned, 

 it is necessary to assume that the cause of the paralysis is something which pre- 

 vents the nerve-impulse from passing from the nerve to the muscle. Micro- 

 Bcopic examination shows that the nerve-fibre does not communicate directly 

 with the muscle-fibre, but end- in-i<le the sarcolemma in an organ which is 

 called the motor end-plate (see Fig. 31). It appears that the nerve acts on the 

 muscle through this organ, ami it> failure to act on the side which was exposed 

 to the curare was because the end-plate had been paralyzed by the drug. By 

 the use of curare, therefore, we are enabled to prevent the nerve-impulse from 

 reaching the muscles, and. when we have done this, we find that the muscle 

 is still able to respond to dired excitation with all forms of irritants, viz., 



1 Ch. Bernard : " Analyse physiologiqne des Pmprietcs dee Systemes tnosculaires et nerveux 

 au moveri du Curare," Otnnptes-rendus, 1856, p. 825. Kolliker: " Physiologische T'ntersuch- 

 ungen iiber den Wirkunjjen einiger (lifte," Archiv fur pdthologische Anatomie, 1S56. 



