194 



Tait and Gunn 



Thus the proximal and distal ends of the nerve were left unaffected by the 

 solution, and to each. of these parts a pair of electrodes was applied. To 

 ensure that the solution should not run along the uncovered parts of the 

 nerve and affect either the proximal or distal ends, the middle portion was 

 kept at a slightly lower level than the two ends. The whole nerve-muscle 

 preparation was kept in a moist chamber. The electrodes were connected 

 by means of a Pohl commutator from which the cross wires were removed 

 with a standard Kronecker coil (original pattern), in the primary circuit 

 of which was an accumulator charged to 4^ volts. 



The result of soaking the nerve for a number of hours (the time varied 

 from two to three hours in our experiments) is to abolish conductivity in 



30 30 3» 



I 



l'i(i. 1 (reduced to two-thirds). —Yohimbine lactate, 2 per cent., applied for 1 hour to 3 cm. of nerve. Proximal 

 stimulation, rate 128 per sec. Intensity, 30 Kronecker units. Rate of drum, 1 mm. per sec. Tracing (2) 

 taken 40 sees, after tracing (1). 



Tracing (1) shows (i.) irregularity of tetanic responses ; (ii.) diminution in height of successive tetanic responses. 

 I'racing (2) shows (i.) diminution in extent of successive tetanic responses with diminishing intervals between stimulations;, 

 (ii.) subsequent improved responses with increased intervals of rest between stimulations. 



the part affected by the yohimbine solution. As is the case when other 

 anaesthetics are applied to nerve, the abolition of conductivity does not 

 occur abruptly but comes on gradually, so that long before the nerve has 

 actually lost the power of conduction, changes can be detected which 

 indicate a depression of function. 



Thus when the proximal end of the nerve is stimulated at some fixed 

 rate lying between 100 and 200 excitations per second, the tetanic 

 responses of the muscle begin to undergo a change ; instead of being 

 smooth-topped, they become irregular in form, and the muscle, instead of 

 remaining in continuous contraction, ultimately twitches more or less 

 spasmodically (see fig. 1). On the other hand, the muscle response to distal 

 stimulation is a smooth and regular tetanus, showing that the irregularity 



