TISSUE FUNCTIONS 707 



Sklarek (1866) noted that arsenite abolishes sensation and reflex activity 

 in frogs, and later reduces voluntary motor activity. Ringer and Murrell 

 (1878) reinvestigated this and found the loss of voluntary power to occur 

 well before the loss of reflexes. The muscles in a frog paralyzed by arsenite 

 still contract to direct electrical stimulation; furthermore, the motor nerves 

 conduct normally during paralysis (Lesser, 1878 c). Thus the block must 

 be either central or on the neuromuscular junction; Ringer and Murrell 

 assumed the former. The data necessary to locate the site of action have 

 not been reported. Arsenite seems to have little effect on nerve axons. 

 Makarov (1927) found complete conduction blockade only after 30-70 

 hr in arsenite concentrations as high as 75-300 mikf, but the results of 

 Lendle and Reinhardt (1931) are quantitatively quite different (see ac- 

 companying tabulation). The nerves in this work are reasonably sensitive 



Concentration for conduction block (m.M) 



but the time required to act is very long. This could be explained on the 

 basis of slow penetration, but it is seen that muscle behaves similarly. 

 Schmitt et al. (1934) showed that whereas arsenite depresses nerve respira- 

 tion rapidly, the effects on the action potential are delayed (see accompany- 

 ing tabulation). That the neural sheath presents a barrier to the arsenite 



was eliminated by showing that a lag period exists after splitting of the 

 sheath. There are probably two reasons for the lag period. One is the fact 



