SIMPLEST NEURAL ARCS. 35 



relatively careful observation. It is, however, in no way analogous 

 to the knee-jerk. It is relatively slow, and is controlled through the 

 autonoDoic system. Furthermore, a series of measurements may give 

 rise to long-continued and painful ocular disturbances, as is known to 

 one of us from unpleasant personal experience. Finally, the best 

 available registering technique for the pupil reflex is by cinematograph, 

 an arrangement that gives too few records per second for accurate 

 measurements of latency. For these reasons, and on account of the 

 necessity of limiting the selection, the pupil reflex was omitted from 

 the present study. 



The protective lid-reflex, on the contrary, seemed to offer a perfect 

 analogy to the knee-jerk. It has a latency of the same order as the 

 knee-jerk, and normally changes very slowly from adaptation. Fur- 

 thermore, entirely adequate and relatively simple technique is avail- 

 able, by which uniform stimuli (sound) can be recorded by the same 

 optical system that records a movement of the shadow of the eyelashes. 

 The resulting photographic records are unusually free from instrumental 

 latency and distortion. 



EFFECT OF ALCOHOL ON THE PATELLAR REFLEX. 



The present investigation of the effect of alcohol on the knee-jerk is 

 based on the assumption that the reflex character of the human knee- 

 jerk has been established. The classical controversy as to the nature 

 of the phenomenon was started by Westphal's 1 contention that there 

 was no evidence for receptors in the muscle. After Westphal's evi- 

 dence was weakened by the discovery of proprio-muscular receptors, 

 Waller 2 and Gotch 3 were led to believe that the knee-jerk was not a 

 reflex because of the exceedingly low latent time that was required 

 under favorable conditions by the knee-jerk of the rabbit. 



The psychiatrists, on the other hand, have long assumed the reflex 

 character of the human knee-jerk. The clinical value of the knee- 

 jerk test is so firmly fixed by the mass of clinical experience that 

 psychiatry may be comparatively indifferent to the question as to its 

 nature. Its diagnostic significance rests secure on empirical correla- 

 tions. Its physiological exploitation, however, was practically impos- 

 sible as long as the uncertainty remained. But if the knee-jerk is a 

 true reflex, it must be of value not only in diagnosis of nervous disease, 

 but also for a large number of studies of the normal physiology of the 

 human reflex arc, such as the rate of propagation of nervous excitation 

 in human nerves and in the cord, for studies of fatigue, inhibition, and 

 "Bahnung," as well as for the effects of drugs on man. 



A number of recent studies have shown conclusively that whatever 

 may be true of the rabbit, the normal human knee-jerk as ordinarily 



HVestphal, Archiv f. Psychiatrie, 1875, 5, p. 803. 

 "Waller, Journ. Physiol., 1890, 11, p. 384. 

 3 Gotch, Journ. Physiol., 1896, 20, p. 322. 



