X 



THE FORE-BRAIN 



551 



chloride and sulphate of sodium. In very weak solutions these 

 have no effect on the faradic excitability of the cortex ; while in 

 stronger concentrations, or solid, they almost constantly lower the 

 excitability. In minimal doses they do not include spontaneous 

 spasms or clonic contractions; in comparatively strong doses, on 

 the contrary, they induce paralytic symptoms, which are evidently 

 due to the chemical destruction of the nerve elements. 



(ft) The second group includes strychnine and picrotoxin. In 

 minimal doses these substances immediately raise the faradic 



Fio. 277. Surface of left hemisphere ot < '< rm- I'm. 278. Upper surface of hemispheres of 



fitli'i'iiK. (Kerrier.) I'fri'iijiillii.-ita. (Kerrier.) 



1, Opposite hind-limb advanced as in walking; 2, movements of thigh, leg, and foot ; 3, move- 

 ments of tail; 4, retraction and adduction of opposite arm; 5, forward extension of opposite 

 arm and hand ; a, b, r, <1, single and combined movements of lingers and list ; (5, supination and 

 llexion of f ore -arm ; 7, contraction of zygomatic muscles with retraction and elevation of angle 

 of mouth ; 8, elevation of ala of nose and upper lip ; !>, 10, opening of mouth, advance of lips, 

 protrusion and retraction of tongue ; 11, retraction of opposite angle of mouth ; 12, wide opening 

 of eyes, dilatation of pupils, movement of eyes and head to opposite side ; 13, 13', movement of 

 ryes to opposite side, with upward or downward deviation and contraction of pupils ; 14,14', 

 pricking of opposite ear, with rotation of eyes and head to opposite side, wide dilatation of pupils. 



excitability of the excitable areas, and after a very 1 rief latent 

 period of from a few seconds to 1-2 minutes produce the localised 

 movements similar to those observed on faradic excitation of the 

 centres, but the movements are repeated rhythmically, at the rate 

 of about 40-50 per minute, for a longer or shorter time (25-35 

 mins.) in the form of characteristic tic-like movements, whether 

 the animal is fixed to the apparatus, or suspended by the back, or 

 left free on the ground. 



Probably curare should also be included in this class of 

 the chemical substances which are capable of directly exciting the 



