468 GENERAL BIOLOGY 



A correlation mechanism within the nerve centers that 

 remain may be demonstrated as follows: stimulate one 

 side of the frog in the flank with the acid, and see the foot of 

 the same side lifted and rubbed against the spot as if to wipe 

 it off. Then stimulate the flank again in like manner, but 

 hold the foot of that side by the toes to keep it from repeat- 

 ing the act. After one or more attempts to use this foot, 

 the foot of the other side will be lifted and swung around to 

 the spot stimulated. 



With an adjustable induction coil and a small battery, 

 try electrical stimuli of gradually increasing strength, to see 

 the spread of the effect with the increase in intensity of the 

 stimulus.* 



Stimulate the cut end of the cord; here are the paths 

 coming down from the brain. Then destroy the cord by 

 thrusting a wire down the vertebral column and twisting it, 

 thus breaking up the reflex arcs and test again for responses. 



Then expose the great sciatic nerve (it will appear as a 

 coarse white thread lying between the muscles of the inner 

 side of the thigh, and stimulate it directly to produce mus- 

 cular response. Then trace this nerve to its forking at the 

 knee, and stimulate each of ito main branches separately to 

 see the specifically different responses resulting. 



The record of thiS st-cidy will consist of notes and diagrams 

 illustrating th^ nature of the experiments performed, and 

 their resulXv«. 



*A little strychnine injected under the skin with a hypodermic 

 svi'inge will greatly increase the sensitiveness of the spinal cord tc 

 cutaneous stimulation : the response, however, soon ceases to be 

 orderly and purposeful, and becomes convulsive. On the other 

 hand a few crystals of salt placed upon the cut end of the cord 

 will check, and after a little time, inhibit altogether the reflex 

 responses: the effect will however soon disappear, upon washing 

 the salt off with normal saline solution. 



