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



435 



violent optical impression. Nitrite of amyl lias no effeet on the jerk, 

 but ether abolishes it in dogs, but has a smaller effect in rabbits. 

 Faradic currents strong enough to produce contraction of muscles 

 increase the knee jerk, and stimulation of the dry skin has a like 

 effect. Short voltaic currents not strong enough to cause muscles to 

 contract are attended by the same result, as are voltaic currents 

 applied to the head, especially the temporal regions and especially 

 when the negative pole is applied. Making is more effectual than 

 breaking the current, and the effects soon wear away. Loug ascend- 

 ing galvanic currents to the spine cause marked increase, while 

 descending cause far less, and moderate currents do not reinforce the 

 knee jerk. These results led these observers to conclude that the 

 knee jerk is a direct muscular act, but that it cannot exist without 

 that spinal contribution known as tone, which is capable of increase 

 by a variety of causes. They consider that it cannot be a reflex, as 

 the latter are inhibited by violent sensory stimulations, which they 

 have shown increase the knee jerk. An exactly opposite view is that 

 taken by Lombard,* who observed that the flexors, i.e., the hamstrings, 

 sometimes contracted when the ligamentum patellae was struck. He 

 concluded that the. flexors were caused to contract by reflex excita- 

 tion, and that the whole phenomenon was of the same nature. 



Bowditch and Warrenf found that when a voluntary action was 

 employed to produce exaltation of the knee jerk the reinforcement 

 wholly depended on the interval between starting of the action and 

 the incidence of the blow to elicit the jerk. When this was pro- 

 longed, instead of being exalted, the knee jerk became much reduced ; 

 the interval at which the effect changes from positive to negative 

 varied from 022 to 06 second. The effect of sudden auditory or 

 visual stimulus was usually positive. Tactile stimulation of the 

 conjunctiva and of the nasal mucous membrane also showed the same 

 effect. 



BastianJ has recently brought forward striking evidence to prove 

 that in man total transverse lesion of the spinal cord above the 

 lumbar enlargement abolishes, instead of augmenting, the knee jerks, 

 as is commonly supposed ; and Bowlby§ has supported this view by 

 the results of his observations in fracture of the spine with crushing 

 of the cord. 



Buzzard || has met with absence of the knee jerk in man when there 

 was extravasation of blood into the cranial cavity. 



* £ Journ. of Physiol.,' vol. 10, p. 122 ; ' American Journal of Psychology,' vol. 1, 

 p. 50, 1887. 



t ' Journ. of Physiol.,' vol. 11, p. 25, 1890. 

 t ' Med. Chir. Trans.,' vol. 73, 1890 ; ' Lancet,' March, 1890. 

 § ' Med. Chir. Trans.,' vol. 73, 1890 j < Lancet,' May, 1890. 

 i| 1 Med. Press and Circ.,' March, 1890. 



