ACTION OF CURARA. 



471 



carbolic acid. 2. The ends of the sartorius of the frog, in which no nerve-termina- 

 tions are observable by means of the microscope, contract when they are stimulated 

 directly (Kilhne). 3. Curara paralyses the extremities of the motor nerves, while 

 the muscles themselves remain excitable (CI. Bernard, Kblliker). The action of 

 cold, or arrest of the blood supply in an animal, abolishes the excitability of the 

 nerves, but not of the muscles at the same time. 4. After section of its nerve, a 

 muscle still remains excitable, even after the nerves have undergone fatty degenera- 

 tion (Brovm-Sequard, Bidder). 5. Sometimes electrical stimuli act only upon the 

 nerves and not upon the muscle itself (BriicJce). [6. The foetal heart contracts 

 rhythmically before any nervous structures are discoverable in it.] 



[The Action of Curara. Curara, woorali, urari, or Indian arrow poison of South America, is 

 the inspissated juice of the Strychnos crevauxi. A watery extract of the drug, when injected 

 under the skin or into the blood of an animal, acts chiefly upon the motor nerve-endings, and 

 does not affect the muscular contractility. An active substance, curarin, has been isolated 

 from it (p. 474). Poison a frog by injecting a few milligrammes into the dorsal lymph-sac. In 

 a few minutes after the poison is absorbed, the animal ceases to support itself on its fore-limbs; 

 it lies flat on the table, its limbs are paralysed, and so are the respiratory movements in the 

 throat. When completely under the action of the poison, the frog lies in any position, limp 

 and motionless, neither exhibiting voluntary nor reflex movements. If the brain be destroyed 

 and the skin removed, on faradising the sciatic nerve, no contraction of the muscles of the hind- 

 limb occurs, but if the electrical stimulus be applied directly to the muscles, they contract, 

 thus proving that curara poisons the motor connections and not the muscles. If the dose be 

 not too large, the heart still continues to beat, and the vaso-motor nerves remain active.] 



[Methods. (1) Local Application. Bernard took two nerve-muscle prepara- 

 tions, put some solution of curara into two watch-glasses, and dipped the nerve 

 into one glass and the muscle of the other preparation 

 into the other glass. The curara penetrated into both 

 preparations, and he found, on stimulating the nerve 

 which had been steeped in curara, that its muscle still 

 contracted, so that the curara had not acted on the motor 

 nerve-fibres ; while stimulation of the nerve of the other 

 preparation produced no contraction, although the corre- 

 sponding muscle contracted. In the latter case, the curara 

 had penetrated into the muscle and affected the intra- 

 muscular portions of the nerve.] 



[(2) But it is the terminal or intra-muscular portions 

 of the nerves, not the nerve-trunk, which are paralysed. 

 Ligature the sciatic artery, or, better still, tie all the 

 parts of the hind-limb of a frog, except the sciatic nerve, 

 at the upper part of a thigh (fig. 315). Inject curara 

 into the dorsal lymph-sac. The poisoned blood will, of 

 course, circulate in every part of the body except the 

 ligatured limb. The shaded parts are traversed by the 

 poison. The animal can still, at a certain stage of the 

 poisoning, pull up the non-poisoned limb, while it cannot Frog with sciatic artery li- 



Fig. 315. 



with afferent and efferent 

 nerves; P., poisoned, N. P., 

 non-poisoned leg ; M, gas- 

 trocnemius muscles. 



move the poisoned one. At this time, although poisoned 

 blood has circulated in the sacral and intra-abdominal 

 parts of the nerves, yet they are not paralysed, so that 

 the poison does not act on this part of the trunk of the 

 nerve. But we can show that it does not act on any part of the extra-muscular 

 trunk of the nerve. This is done by ligaturing the arteries going to the gastrocnem- 

 ius muscle, and then poisoning the animal. On stimulating the nerve on the 

 ligatured side, the gastrocnemius of that side contracts, although the whole length 

 of the nerve-trunk was supplied by poisoned blood. Therefore, it is the intra- 

 muscular terminations of the nerves which are acted on.] 



