iv GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 263 



The grey matter of the centres is capable of reacting by pro- 

 longed excitation to a simple stimulus, e..g. the prick of a pin. 

 Thus Birge observed that the rat's spinal cord reacted by simple 

 twitches to puncture of the white matter and by a regular tetanus 

 to puncture of the grey matter. Again, the frog's spinal cord 

 responds by prolonged excitation to single induction shocks 

 (Marchand). According to Baglioni and Fienga the motor 

 elements of the ventral horn exhibit the same property as the 

 frog's spinal cord, of reacting to single stimuli by tetaniform 

 excitation. 



Another charactistic property of the grey matter is that it 

 reacts more effectively to frequent and weak stimuli than to 

 stronger and less frequent shocks. Kronecker and Nicolaides, on 



FIG. Ki4. Reflex movement of frog's leg after electrical stimulation. (Stirling.) The lower line 

 marks seconds ; the middle line the duration of the stimulation ; the upper line the reflex 

 movement preceded by small preliminary contractions. 



stimulating the vasomotor centre, obtained feeble effects with 

 strong but infrequent induction shocks, while with moderate but 

 more frequent shocks of the same current the effect was much 

 more pronounced. The same appears in reflex stimulation of the 

 spinal cord ; break induction shocks of a given strength induce 

 reflex movements more rapidly in proportion to their frequency 

 (Stirling). With this property is intimately associated that of 

 summation of stimuli possessed in a striking degree by the grey 

 matter ; this gives the character of a high tension discharge to 

 the reaction. Sanders -Ezn with chemical stimuli, Stirling with 

 electrical stimuli, applied to the skin of the decerebrated frog, 

 obtained small preliminary contractions and then a vigorous 

 contraction, which is succeeded by a period of exhaustion, necessary 

 to the formation of a new charge (Fig. 164). 



Lastly, artificial excitation of the grey matter shows that it has 

 the faculty of transforming the rhythm of the stimulation into a 

 different and characteristic rhythm of its own. This is seen from 



