NERVE 515 



spasms of the leg-muscles, etc., will be seen, increasing in force. Soon 

 the extensor muscles begin to overcome the flexors, and shortly the legs 

 are rigidly straight. Note the extreme irritability of the whole animal 

 (due to abnormal stimulation of the cord by the alkaloid) : a slight pinch 

 of the skin causes universal convulsions. Now destroy carefully with 

 the seeker the spinal cord, and note that the previously noted phenomena 

 cease at once. Strychnine acts on the spinal cord alone. 



The precise mode of action chemically of strychnine on the nerve-cells 

 is unknown, but whatever it may be, the drug collects especially in the 

 spinal cord, and violently stimulates the reflex motor nerve cells. Any 

 influence which can disturb the equilibrium of these centers, then, causes 

 strong tonic spasm (contraction) of the muscles. It is apparently wholly 

 owing to the fact that the extensor muscles are more powerful than the 

 flexors that the resulting position of the animal is one of extreme extension. 

 The practical importance of acquaintance with the phenomena of strych- 

 nine-poisoning should not be lost sight of. 



FIG. 284 



Stimulation of the uncut vago-sympathetic in the frog. The weak stimulation lasted between 

 the little squares on the stimulation-line, and the effect took place only about twelve seconds 

 later. To be read from left to right. The time-line is in seconds. 



Expt. 85. Augmentation of Function. (Apparatus : Frog-board, in- 

 ductorium, shielded stimulating electrode, heart-lever, kymograph, chro- 

 nograph, etc., signal.) One of the best examples of neural augmentation 

 is the effect of the sympathetic on the heart. To expose the sympathetic 

 nerves which influence the frog's heart, pith a frog's or toad's brain, 

 fasten the animal on the frog-board, cut away the lower jaw completely, 

 and excise it below the angles. Very carefully remove tissue until the 

 upper part of the spinal column is completely bared. Now very care- 

 fully raise and cut through the flat strip of muscle (the levator anguli 

 scapulae) extending obliquely outward from the occipital bone. This 

 exposes the vago-sympathetic, the vagal ganglion, and the sympathetic 

 line extending upward from the second, third, fourth, and fifth vertebrse. 

 (This ascending trunk is usually pigmented and accompanied by an 

 artery.) Ligate the nerve as low as possible and cut it below the ligature. 

 Keep the nerves moist with modified Ringer's fluid. Expose the heart 

 and place it in the heart-lever arranged to write on the very slowly rotating 

 drum. (The writing end of the lever should ordinarily move at least 



