476 



ANNALS NEW YORK ACADEMY OF SCIENCES 



choline and other chemical agents on ganglion cells. For example, the 

 frequency of impulses initiated by a certain concentration of acetyl- 

 choline may be reduced by increasing the concentration of calcium in 

 the perfusion fluid, or by reducing the concentration of potassium (fig- 

 ure 17). Conversely, the frequency of discharge may be increased by 



2 X NORMAL 

 CALCIUM 



5 X NORMAL 

 POTASSIUM 



i«iw 



'■°'""'-ii i ii|i|iiiiiii li ii i II m ill mi l m i l 



NORMAL 



!il ill lli ll l l ll ll l ll li l l i ||l|ll l ll | ll lllll l l i 44^ 



4 



NO CALCIUM 



NO POTASSIUM 



Figure 17. Impulses discharged from a single cell in a cat's stellate ganglion, during perfusion 

 with six different solutions, all containing the same amounts of acetylcholine (40 /xg. 1 cc), but 

 different concentrations of calcium and potassium. Time in seconds. 



lowering the concentration of calcium or by augmenting the concentra- 

 tion of potassium. These effects of calcium and potassium on the 

 rhythmic action initiated by another chemical agent might be antici- 

 pated from our knowledge of their effects on the electrical excitability 

 of axons. It is, perhaps, worthy of comment that, regardless of whether 

 the acetylcholine, calcium, and potassium act upon the same or different 

 parts of the irritable mechanism, their combined effects become mani- 

 fest in a modification of the rhythmic process which initiates the 

 propagated impulses. 



This repetitive process, which is a latent characteristic of nerve, is 

 revealed in the discharge of impulses initiated by sensory stimulation 

 or by chemical action. It is also to be observed in the periodic activity 

 of nerve cells which are excited by the arrival of impulses in adjacent 

 pre-synaptic endings. When the preganglionic fibers entering a sym- 

 pathetic ganglion are stimulated by repetitive electrical shocks of high 

 frequency, the cells discharge repetitively, but at a much lower fre- 



