400 INDEPENDENT MUSCULAR IRRITABILITY. 



fore limbs or trunk above the ligature may produce movements 

 in tin' hind limbs, but in no other part of the body. 



These facts are intelligible only on the hypothesis that the 

 urari has destroyed (or suspended) the irritability of the 

 motor nerves in that part of the body to which, by means of 

 the blood current, it has had access, but has not destroyed the 

 irritability of the sensory nerves or of the central nervous sys- 

 tem. Pinching the skin of the fore limb gave rise to an affe- 

 rent nervous impulse which, either by volition or by reflex 

 action, gave rise in turn to efferent impulses which were unable 

 to manifest themselves through the poisoned motor. nerves of 

 the fore limbs and trunk, but found vent through the unpoisoncd 

 motor nerves of the hind limbs. 



In order to bring these results out well, the dose of poison 

 must not be more than sufficient to poison the motor nerves. 

 Subsequent or stronger action of the poison affects the central 

 nervous system as well. 



Obs. III. In a fresh, strong frog, lay bare the sciatic nerve 

 on one side say the right in its lower course, place a ligature 

 under it near where it divides into its two brandies, and tic 1 tl 

 ligature tightly round the leg above the knee. Thecircnlati 

 of the lower right leg will thus be completely arrested; but 

 asmufh as the nerve is not included in the ligature, there wij 

 be complete nervous connection between the right lower leg an< 

 the rest of the body. Poison with urari. As soon as tH 

 animal has come under the influence of the poison, det^tmine 

 the following facts : 



Complete absence of spontaneous movements, except per- 

 haps some feeble stirring of the right lower leg. 



Stimulation of the right lower foot may produce movements 

 in the right lower leg, but will not produce movements in any 

 other part of the body. 



Stimulation of any part of body may produce movements in 

 the right lower leg, but in no other part of the body. 



If the two sciatic nerves be laid bare along their whole 

 course, it will be found that stimulation, however strong, 

 applied to the left sciatic nerve, produces no contractions 

 whatever in the muscles to which its brandies go; while 

 stimulation, even slight, of the right sciatic nerve, whether 

 applied above or below the level of the ligature, and even 

 close up to the spinal cord, produces contractions in the mus- 

 cles of the right lower leg, but in none other. 



Now the whole of the trunk of the right sciatic nerve, being 

 supplied with poisoned blood, has been as much subject to the 

 influence of the urari as the left sciatic. Nevertheless, while 

 the trunk of the left sciatic seems to have entirely lost its 

 irritability, that of the right seems to have suffered very little 

 indeed. The difference really is, that the left sciatic trunk 



