412 



THE SPINAL CORD. 



Fig. 137. 



tered ; and 2d, that the motor and sensitive nervous filaments may 

 be paralyzed independently of each other. The above facts are 

 shown by the three following experiments : 



1. In a living frog (Fig. 137), the sciatic nerve (N) is exposed in 

 the back part of the thigh, after which a ligature is passed under- 

 neath it and drawn tight around the bone and the remaining soft 

 parts. In this way the circulation is entirely cut off from the limb 

 (d), which remains in connection with the trunk only by means of 

 the sciatic nerve. A solution of sulphocyanide of potassium is then 



introduced beneath the skin 

 of the back, at I, in sufficient 

 quantity to produce its speci- 

 fic effect. The poison is then 

 absorbed, and is carried by 

 the circulation throughout the 

 trunk and the three extremi- 

 ties a, b, c ; while it is pre- 

 vented from entering the limb 

 d, by the ligature which has 

 been placed about the thigh. 

 Sulphocyanide of potassium 

 produces paralysis, as we have 

 previously mentioned, by act- 

 ing directly upon the muscu- 

 lar tissue. Accordingly, a gal- 

 vanic discharge passed through 

 the limbs a, b, and c, produces 

 no contraction in them, while 

 the same stimulus, applied to 

 d, is followed by a strong and 

 healthy reaction, But at the 

 moment when the irritation 

 is applied to the poisoned 

 limbs a, b, and c, though no 

 visible effect is produced in 

 them, an active movement 

 takes place in the healthy 

 limb, d. This can only be 

 owing to a reflex action of the spinal cord, originating in the inte- 

 gument of a, b, and c, and transmitted, by sensitive and motor fila- 

 ments, through the cord to d. While the muscles of the poisoned 



