528 COMPARATIVE ELECTRO-PHYSIOLOGY 



magnetic arrangement, can be maintained in a state of to- 

 and-fro oscillation, always strictly parallel to the primary. 

 The recording-index moves in a vertical plane, and the 

 smoked plate backwards and forwards, at right angles to 

 this, the extent of its oscillation being about I mm. The 

 recording point is adjusted, barely to touch the smoked 

 surface. Thus the oscillation of the plate brings it periodi- 

 cally in contact with the tracing-point, which is thus practi- 

 cally free to execute its movements unimpeded. When the 

 oscillation frequency of the plate is sufficiently high, and the 

 speed of the recording-surface low, the curve of record 



FIG. 323. Pho ographic Reproduction of Record of Mechanical Re- 

 sponses of Frog's Nerve (left-hand record) and Plant-nerve (right-hand 

 record) obtained on Smoked Glass Surface of Oscillating Recorder 



appears as continuous. In other experiments, where the 

 determination of time-relations is important, a high speed 

 can be given to the plate by the regulation of the clockwork, 

 and the record will then appear as a succession of dots. 

 From these, arid a knowledge of the oscillation-frequency 

 of the plate, the time-relations of different parts of the curve 

 can be determined with accuracy. I give here two different 

 series of uniform mechanical responses recorded with this 

 instrument, obtained from the nerves of frog and of fern 

 respectively (fig. 323). 



I have also been able, by means of this instrument, to 

 demonstrate a very important fact, namely, that the responses 



