98 STRYCHNINE REACTION 



strychninized by placing them for a few minutes in a solution of strych- 

 nine sulfate (1 : 10,000), mechanical stimulation produces the opposite 

 effect; viz., extreme extension and activity of the animal. The action 

 of tlje strychnine is, therefore, to convert the inhibition of the trans- 

 verse and circular muscles in the normal response into an excitation. 



Experiments on the Starfish, Asterias Jorhesii. 



Animals which orient themselves by means of contact sensitivity or 

 stereotropism are in a state of motor equilibrium when their sensitive 

 (ventral) regions are in contact with a surface. When this normal 

 relationship is disturbed, as by putting the animal on its back, rapid 

 and exaggerated body movements take place, until by chance, the 

 specific receptors come into contact with a surface. Immediately 

 from this point of contact excitatory and inhibitory impulses are sent 

 out, the effect of which is to bring the animal without further waste 

 effort into its normal orientation again. 



In the starfish the tube feet are the stereosensitive organs. In an 

 inverted specimen of normal vigor all the arms show initial twisting 

 movements. From the arm whose tube feet first get into contact 

 with a solid surface an excitatory impulse starts to an adjacent arm, 

 as from A to B (Fig. 1), causing the latter to twist as so to face A 

 ventrally and to attach its tube feet to the solid surface. Inhibitory 

 impulses passing from A to D and from B to C cause D and C to 

 release any initial hold they may have had and to bring E more or less 

 passively with them, thus turning a somersault over A and B.^ 



This reaction evidently implies reciprocal innervation. If it were 

 possible to reverse the functioning of this system by means of strych- 

 nine, we would have a still closer parallel with the corresponding 

 mechanism in vertebrates. The similarity of the reaction of the 

 earthworm to that of the vertebrate in this respect, is perhaps to be 

 expected since the histology of the nervous system of the annelid 

 also shows the synaptic structures. But because the nerve tracts of 

 the starfish do not contain elements histologically similar, we must 

 suppose that the strychnine acts, if it acts at all, on certain chemical 

 elements of the neuron, rather than upon some special anatomical 



^ Moore, A. R., Biol. Bull., 1910, xix, 2?>S; Am. J. Physiol., 1910, xxvii, 207. 



