SIMPLEST NEURAL ARCS. 



43 



progression of the thickening wave. With our recording device, how- 

 ever, that progression is entirely irrelevant, since we measure from the 

 moment of stimulation of any part of the muscle to the moment of the 

 reflex thickening of that particular part. Since both events are re- 

 corded by the same writing lever, the record as it stands is an exceed- 

 ingly accurate measurement of the latency of the particular arc which 

 is involved in the reflex action of that part of the muscle. The vertical 

 displacement of the recording line indicates the amount of the reflex 



FIG. 5. A typical record of the pateilar reflex. 



muscle thickening, multiplied by the leverage of the recording-arm. 

 We believe that these reflex measurements are particularly well adapted 

 to indicate the relative changes induced in latency and amount of this 

 reflex arc by the use of drugs. 



Each line represents the reflex response to a double stimulation of 

 the same intensity. The interval between the lines is one complete 

 revolution of the drum. Since this was regulated to occur in 5 seconds, 

 the series of records follow in pairs at intervals of 5 seconds. Differ- 



