iv GENERAL PHYSIOLOGY OF NEEVOUS SYSTEM 265 



More recently (1909) Baglioni has brought forward other 

 experimental arguments in support of the theory of the elective 

 action of these two poisons, and employed the cerebrospinal axis of 

 the toad, which, unlike that of the frog, can be completely isolated 

 and removed from the vertebral cavity owing to the great length 

 of its cauda equina. It allows all the operative handling 

 necessary for the complete isolation of the cerebrospinal axis, 

 which in the frog involves serious lesions and even death of the 

 central substance, since this is extremely sensitive to the least 

 mechanical injury. In the central preparation of the toad (Fig. 166) 

 it is comparatively easy to apply small wads of cotton wool soaked 

 in strychnine or carbolic acid to the dorsal or ventral surface of 

 the lumbo-sacral enlargement, which contains the centres of reflex 

 activity for the posterior limbs. It is found that strychnine pro- 

 duces increased reflex excitability and tetanic spasms when applied 

 to the dorsal surface of this part, while it is inert when placed in 

 direct contact with the ventral surface. Vice versa, carbolic acid, 

 in a weak solution (O'l per cent) increases reflex excitability and 

 produces clonic convulsions when applied to the ventral surface, 

 while it has no such effect when brought into direct contact with 

 the dorsal surface. By this means Baglioni also demonstrated 

 the presence of central elements on the dorsal surface of the bulb, 

 which, under the local action of strychnine, induce tetanus in 

 the posterior limbs. 



Baglioni confirmed the interpretation already given by Claude 

 Bernard of the origin of the tetanic spasms observed during the 

 action of strychnine. The essential cause is the abnormal increase 

 of reflex excitability produced by strychnine, owing to which 

 minimal peripheral sensory stimuli, which are incapable under 

 normal conditions of inducing reflex contractions, are now adequate 

 to excite all the centres of the cord which they affect, to the point 

 of exhaustion. If after severing the spinal cord from the bulb the 

 whole of the dorsal roots are cut (as was also seen in 1893 by 

 H. E. Hering), or if every peripheral stimulus from the skin and 

 the higher sense organs is artificially eliminated by placing the frog 

 in a suitable medium, strychnine will kill the animal without pro- 

 ducing any tetanic spasms. While the stimuli from the skin and 

 external sense-organs induce the primary contraction of all the 

 muscles of the body, it is the secondary stimuli coming from the 

 end organs seated in the muscles and tendons stimulated by the 

 muscular twitches that reflexly incite the subsequent tetanic con- 

 vulsions, till the temporary or final fatigue of central activity is 

 brought about. 



That under normal conditions the spinal cord is not capable of 

 reacting by a prolonged series of tetanic contractions to faradic 

 stimuli applied to afferent fibres is due to the fact that after each 

 single excitation the central elements are thrown into a refractory 



