30 CHEMICAL STIMULATION OF THE NERVE CORD 



phyla develops hand in hand with increasing complexity of the 

 nervous system. 



By such a method it seems possible to discover similarities and 

 relationships in the chemical constitution of neurons which would 

 otherwise remain undetected. With this purpose in view experiments 

 have been carried out on chemical stimulation of the nerve cord of 

 the earthworm, Lumhricus terrestris. 



In an experiment the animal was decapitated, pinned down by the 

 anterior end and the anterior portion of the nerve cord laid bare for 

 a distance of about 2 cm. A piece of cord about 1 cm. in length 

 was then separated from the underlying tissue. The substance to 

 be tested was applied to the loosened part. Stimulation was shown 

 by spasmodic squirming of the posterior segments of the worm. 

 Control experiments were made by applying the stimulating substance 

 to a part of the body wall after removal of the nerve cord from that 

 section of the worm. No reaction of the posterior segments resulted. 



It is of course impossible to separate the nerve cells from their 

 processes in this form. Therefore excitants of the first class,^ i.e., 

 calcium precipitants and barium salts, were effective in causing 

 stimulation. BaCl2 and KCl in concentrations isosmotic with the 

 worm's blood caused strong responses immediately. Responses due 

 to the action of Na2S04 and Nas citrate were weaker but unmistak- 

 able. Tetra-ethyl-ammonium chloride in m/64 concentration made 

 up in Ringer solution acted as a powerful excitant. 



Of the substances belonging to the second group, camphor in one- 

 fifth saturated solution, strychnine in saturated solution, atropine 

 sulfate in m/8 concentration and picrotoxin crystals all caused strong 

 reactions. But creatine, caffeine, and nicotine phenol had no stimulat- 

 ing action. Creatine, caffeine, and phenol were applied to the nerve 

 cord in the form of crystals and solutions; nicotine in concentrations 

 of 0.004 per cent and 0.4 per cent was made up in isosmotic Ringer 

 solution. 



When chemical excitation did take place the response was almost 

 immediate — within a minute of the time of application. This is 

 a noteworthy fact since in chemical stimulation of the mammalian 

 cortex the latent period is 10 or 15 minutes and the latent period for 



