42 PSYCHOLOGICAL EFFECTS OF ALCOHOL. 



the contact-breaker was tested by one free revolution of the drum, but 

 without letting the hammers fall. When all these details were in order, 

 the operator touched the key to the mechanism which gave the rotating 

 smoked drum a gradual lateral displacement, so that the succession of 

 knee-jerk records appeared as one continuous line whose base was a 

 spiral. .Alter each stimulus the operator caught the hammer on its 

 rebound from the knee and raised it to the magnet. If more than one 

 stimulus weight was used, the record regularly began with the lighter. 

 The pendulum bobs were then progressively increased in weight until 

 a vigorous reflex was produced. For all except the earliest records, 

 two or more stimulus weights were regularly used in each period. 

 Unless this had been done, it would frequently have occurred that the 

 reflexes at some period of the experimental session would have had no 

 comparable "normal of the day." For example, it frequently, almost 

 regularly, happened during an experimental session that, after an hour 

 or two of relative quiet, the knee-jerk was notably decreased in extent. 

 Occasional!}-' a stimulus that at first produced a good reflex later 

 produced no reflex at all. If that stimulus alone had been used, either 

 the later experiments would be meaningless, or the stimulus must be 

 changed at some time during the session, with consequent incom- 

 parability of earlier and later results. 



In the record shown in figure 5, reading the upper line from left to 

 right, the mechanical shock to the muscle, which is produced when the 

 pendulum hammer strikes the tendon, is recorded by the first slight drop 

 in the base-line. In reading the records for the latent time of the reflex, 

 this point is taken as the moment of stimulation. Owing to the delay 

 which is occasioned by the progression of this mechanical wave along 

 the partially elastic muscle-tissue, this curve does not represent the 

 exact moment when the pendulum strikes the tendon. As measured 

 by Dodge 1 in his own case, there is a delay between the two events of 

 about 3cr. While it does not represent the moment when the tendon 

 was struck, this first dip of the line does represent with greatest preci- 

 sion the much more significant moment when the particular part of the 

 muscle suffered deformation as a result of the blow. And since the real 

 stimulus of the muscle receptors is due to the sudden muscle deforma- 

 tion, as we have mentioned before, this indicator of muscle deformation 

 shows the moment of actual stimulation of the corresponding receptors 

 more accurately than as though we recorded the moment of contact 

 between hammer and tendon. 



The moment of reaction is indicated by the main drop in the line. 

 Here again we are not recording the beginning of change in the muscle 

 as a whole, but rather the reflex thickening of the muscle at exactly 

 the point where we have previously recorded its stimulation. Records 

 from several places along the axis of the muscle show a measurable 



, Zeitschr. f. allg. Physiol., 1910, 12, p. 1. 



