10 LOMBARD :
The Diagnostic Importance of the Knee-Jerk. It is now nine years since Westphal and Erb pro- claimed the absence of the knee-jerk in Tabes Dor- salis, and during this time physicians have come to regard the test as a part of the regular routine of physical diagnosis. Nevertheless they have never been quite satisfied with it. In spite of the fact that Berger reported, as a result of the examination of 1409 healthy individuals, that it was absent in only 1.56 per cent., and that Bernhardt stated that he had found it absent in all but two of forty-six cases of Tabes, which he had studied, there have been so many contradictory reports in medical journals, and every practitioner has found so much difficulty in getting satisfactory results in the doubtful cases, that the knee-jerk has been gradually drifting into disfavor. It is probable that a reaction is at hand, for the discoveries of the past four years offer an explanation of many of the apparently inexplicable results, and at the same time greatly extend the use- fulness of the symptom.
Eeenforcement of the Knee-Jerk. — In 1883 Ernst Jendrassik 1 reported his observation that if the hands were clinched just before the liga- mentum patellaB was struck, the resulting knee-jerk was greater than it was when the subject was quiet.
Jendrassik's interesting discovery was made the subject of the most careful study by Dr. S. Weir Mitchell and Dr. Morris J. Lewis, 2 and they were
^eitrage zur Lehre vondenSchnenreflexen. — Deutsches Archiv. f. klin. Med. Bd. 33, s. 177, 1883.
2 Physiological Studies of the Knee-jerk and of the Reactions of Muscles under Mechanical and other Excitants. — The Philadelphia Medical News, Feb. 13 and 20, 1886.
