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



431 



state on the knee phenomenon, as a subject likely to be fruitful. 

 The adoption of his early advice led to the investigation of many 

 other points of noteworthy interest. I am also much obliged to 

 Professor Horsley for suggestions, especially with regard to control 

 experiments and operative procedures. 



Since Brown- Sequard* described the condition expressed by him 

 under the term spinal epilepsy, the so-called deep or tendon reflexes 

 have attracted considerable attention, and have been the object of 

 numerous investigations. 



Charcot and Yulpianf were the first to accurately describe the 

 phenomenon known as ankle clonus. 



Bouchard £ next observed the arm reflexes, and Erb§ and Westphal 

 simultaneously directed their attention to the contraction of the 

 quadriceps extensor which follows percussion of its tendon. Erb 

 looked on the phenomenon as a reflex, while Westphal considered it 

 the result of direct excitation of the muscle percussed or pulled at 

 its extremity. 



Joffroy endeavoured to prove that cutaneous excitation often 

 evoked the phenomenon, and this view was not refuted until it was 

 shown that it could be evoked in animals by percussion of the 

 denuded tendon. 



Westphal pinched, pricked, and irritated the skin in various ways 

 without producing the knee jerk; a fold of skin lifted away from the 

 tendon and subjected to blows with a hammer was attended with a 

 like negative result. On the other hand, when the skin lying over 

 the ligamentum patellae was frozen by means of Richardson's process 

 the contraction which followed a blow on the tendon was in no way 

 lessened; nor was it where cutaneous anaesthesia existed in non- 

 tabetic cases. 



It soon became evident to observers that the knee jerk is a normal 

 phenomenon, while ankle clonus is only met with in association with 

 abnormal states ; but there was some discrepancy of opinion as to 

 whether the knee jerk is always present in healthy subjects. Berger|| 

 noted its absence in 1*567 per cent, of normal individuals; while in 

 over 200 instances Eulenberger^" never failed to elicit it in the newly 

 born at various ages, and Gowers** states that it is probably never 

 absent in health. 



* ' Journ. de la Physiol.,' vol. 1, p. 475, 1858. 



t ' Soc. Med. des Hop./ May, 1866; ' Union Med.,' p. 464, 1866. 



X 1 Arch, de Med.,' vol. 2, p. 290, 1866. 



§ 'Arch. f. Psych, et Nerven.,' vol. 5, p. 792; ibid., vol. 5, p. 803, 1874; 

 ' Comptes Eendus et Mem. de la Soc. de Biol.,' Series VI, vol. 2, p. 61, 1875. 

 || ' Centralbl. f. Nervenheilkunde,' 1879. 



If ' Correspondenz-Blatt f. Schweizer. Aerzte,' Nos. 1 and 2, 1879. 

 ** ' A Manual of Diseases of the Nervous System,' 2nd Ed., vol. 1, p. 431. 



