214 KANSAS UNIVERSITY SCIENCE BULLETIN. 



nemious muscle. Such contractions instantly ceased when 

 the block circuit was closed, and reappeared immediately when 

 it was broken. 



The strength of the current necessary to block the impul.se.s 

 varied from eight to twenty-five volts, depending upon the 

 kind of stimuli and also upon the condition of the frog. The 

 strongest tetanic contractions produced by stimulating the 

 sciatic nerve with the faradic current, in frogs in good con- 

 dition, required, as a rule, about twenty volts in the block 

 circuit. 



Strychnine tetanus was inhibited with weaker currents, as 

 were also efferent impulses reflexly produced by stimulating 

 either the foot or nerve of the opposite leg. 



Any of the legs can be severed without causing reflex con- 

 tractions in the leg to which the block current was sent, or by 

 placing the tripolar block on its innervatory nerve above the 

 cut. 



The tripolar block can be applied repeatedly both to cut and 

 intact nerves, with but slight, if any, after effects upon the 

 functions of the nerve. 



Afferent impulses were inhibited by currents of only one- 

 tenth of the strength necessary for efferent fibers. 



In every case the efficiency of the block was proved also by 

 the absence of action currents beyond the block. 



The advantages of the tripolar block, as compared with the 

 others that were investigated, are readily seen when we con- 

 sider that it requires about one hour before magnesium sul- 

 phate or cocaine produce an efficient block, and they have an 

 injurious after effect upon the function of the nerve. How- 

 ever, they act alike on both cut and intact nerves ; and that the 

 freezing mixtures, especially liquid air, require several min- 

 utes before they produce blocking, and many more before their 

 effect passes off, although the freezing may be applied re- 

 peatedly without injurious after effect upon intact nerves. 



But it is interesting to note that freezing the nerves, either 

 before or after cutting them, destroys their function at the 

 blocked area. This fact is one of the conspicuous differences 

 between the different blocks experimented with. 



The tripolar galvanic block current, therefore, proved supe- 

 rior to the others in several respects. It may be employed in- 

 definitely on both cut and intact nerves, acts instantaneously, 



