1893.] the Normal State of the Knee Jerk is altered. 433 



Burckhardt,* in attempting to prove that the phenomenon is a 

 reflex, measured the time which elapsed between the percussion of 

 the tendon and the resulting muscular contraction. His investiga- 

 tions led him to the conclusion that it is a reflex which is produced 

 in the spinal ganglia and not in the cord. Following him, numerous 

 investigators endeavoured to determine the time which elapses be- 

 tween the stroke and the contraction. 



Brissaud,f with Franck, measured the time very exactly in healthy 

 persons, and also in those the subjects of disease. These observers 

 found that 0*05 second elapses in healthy subjects, but that it 

 varies from time to time in the same individual, and is modified by 

 conditions which alter the excito-motor properties of the spinal cord. 

 When the lateral columns of the cord are sclerosed the time is 

 diminished ; it is the same on the two sides in a healthy subject, but 

 is less on that side when one lateral column is more sclerosed than its 

 fellow. 



Dejerine'sJ observations and Ter-Meulen's§ researches furnished 

 very similar results. 



Gowers,|| who registered the movement of the limb in his 

 observations, concluded that 0"09 to 0*015 second is the time which 

 elapses between the stroke on the tendon and the resulting move- 

 ment of the limb, which time is sufficient to allow a reflex to occur. 

 Percussion of the tibialis anticus gave a response in 0'03 to 0"04 

 second, which is not sufficient for a cord reflex. He therefore con- 

 cluded that ankle clonus is a phenomenon of direct excitation, while 

 the knee jerk is to be looked on as a reflex. 



Waller^" found that the time which elapsed between percussion of 

 the tendo Achillis and contraction of the gastrocnemius was 0'3 to 0*4 

 second, and in the case of the quadriceps extensor and its tendon 

 03 to 0*4 second. While admitting the necessity of the integrity of 

 the spinal cord for its production, he did not admit its reflex nature, 

 as the time was too short for a reflex to occur. He looked on the 

 phenomena as merely peripheral reactions, and only tests of spinal 

 conditions in the sense that other peripheral reactions of muscles 

 (electrical or mechanical) are tests of these conditions. 



Since then new facts with regard to the knee jerk have been re- 

 corded by several observers. 



* " Ueber Sehnen-Reflexe," ' Festseh. V. Haller,' Bern. 1877. 

 t ' Recherches Anatomo-path. et Physiol, stir la Contracture perm, des Heinipl./ 

 Paris, 1880. 

 X 1 Comptes Eendus,' May, 1878. 



§ ' Ueber Reflexprikkenbaarliied en Pessreflexen,' Amsterdam, 1879. 

 i! « Lancet,' Part I, p. 156, 1879. 

 1 ' Brain,' Part X, 1880. 



