636 COMPARATIVE ELECTRO-PHYSIOLOGY 



response to individual stimulus is abnormal positive. In 

 consequence of stimulation, however, we have seen this 

 relaxation to be arrested, and to pass into growing con- 

 traction. The characteristic of response at this transitional 

 stage is to be diphasic, passing gradually into the normal 

 negative. On reaching this, the B phase, the responses, as we 

 have seen, commence with feeble normal, arid undergo a 

 staircase increase. We may arrive at an idea of the rate of 

 molecular transformation, in this and succeeding phases, 

 from the curve of the mechanical response of nerve under 

 tetanisation (cf. fig. 313). We there saw that in the B, or 

 transitional, phase, the rate of contraction was very rapid ; 

 we also found the individual responses at this stage to show 

 a staircase effect. The rate of contraction next became 

 slower, and the curve was afterwards more or less horizontal. 

 Beyond this, fatigue-relaxation set in. 



We have now to observe the responsive variations 

 characteristic of these different phases. For this purpose, a 

 high magnification of three hundred times has to be em- 

 ployed. Records so obtained are given in fig. 394. The 

 method of procedure is as follows : We first take two or 

 three test-responses to individual stimuli of definite intensity, 

 at the A phase. This test-stimulus is subsequently main- 

 tained at the same intensity. When the record of the A 

 stage has thus been taken, continuous stimulation is applied 

 for a time, till we arrive at the B stage, when the record of 

 responses to individual stimuli is taken once more. The 

 contraction due to the previous tetanising stimulus employed 

 for the conversion of phase, is now so great that the record- 

 ing spot of light is carried out of the field. At the com- 

 mencement of each phasic record, therefore, the spot has to 

 be brought back to the plate by suitable adjustment of the 

 reflecting mirror. Thus the first record of each series really 

 shows the effect of the termination of tetanisation, the sub- 

 sequent records showing response to individual stimuli. We 

 may, however, obtain some idea of the characteristic changes 

 occurring in the nerve as a whole, by joining the tops of the 



