660 FUNCTIONS OF THE SPINAL CORD. [OH. XLVII. 



Reflexes in a Brainless Frog. 



After destruction of the brain the shock of the operation ren- 

 ders the animal for a short time motionless and irresponsive to 

 stimuli, but in a few minutes it gradually assumes a position 

 which differs but little from that of a living conscious frog. If 

 thrown into water it will swim ; if placed on a slanting board it 

 will crawl up it (Goltz) ; if stroked on the flanks it will croak 

 (Goltz) ; if it is laid on its back, and a small piece of blotting- 

 paper moistened with acid be placed on the skin, it will generally 

 succeed in kicking it off; if a foot is pinched it will draw the 

 foot away ; if left perfectly quiet it remains motionless. 



The muscular response that follows an excitation of the sur- 

 face is purposive and constant, the path along which the impulse 

 is propagated being definite. 



Under certain abnormal conditions, however, the propagation 

 of the impulse in the cord is widespread, the normal paths being, 

 as it were, broken down. This is seen in the convulsions that 

 occur on slight excitation in animals or men who have suffered 

 from profuse haemorrhage, or in the disease called lockjaw or 

 tetanus. Such a condition is easily demonstrable in a brainless 

 frog under the influence of strychnine : after the injection of a 

 few drops of a i per cent, solution under the skin, cutaneous 

 excitation no longer produces co-ordinated muscular responses, but 

 paroxysms of convulsions, in which the frog assumes a charac- 

 teristic attitude, with arms flexed and legs extended. 



Spreading of reflexes. If one lower limb is excited, it is that 

 limb which responds : if the excitation is a strong one it will 

 spread to the limb of the opposite side, and if stronger still to 

 the upper limbs also. 



Cumulation of reflexes. This is well illustrated by Turck's 

 method. If a number of beakers of water are prepared, acidulated 

 with i, 2, 4, fec. parts of sulphuric acid per 1,000, and the tips 

 of the frog's toes are immersed in the weakest, the frog at first 

 takes no notice of the fact, but in time the cumulation or sum- 

 mation of the sensory impulses causes the animal to withdraw its 

 feet. If this is repeated with the stronger liquids in succession, 

 the time that intervenes before the muscles respond becomes less 

 and less. This method also serves to test reflex irritability when 

 the frog is under the influence of various drugs. 



Inhibition of reflexes. If, instead of the whole brain, the cere- 

 brum only is destroyed, and the optic lobes are left intact, response 

 to excitation is much slower, the influence of the remaining part 

 of the brain inhibiting the reflex action of the cord. Or if in 



