1893.] the Xormal State of the Knee Jerk is altered. 437 



entirely original on the part cf Prevost, and deserve careful notice. 

 He found that in the cat deep chloroform narcosis, and the adminis- 

 tration of curara, each individually caused abolition of the knee jerk, 

 while profound ether narcosis, almost np to the point of cessation of 

 respiration, failed to do so. In the rabbit, on the other hand, pro- 

 found ether narcosis abolished the knee jerk. Intravenous injection 

 of 1 gramme of chloral in 10 grammes of water, injected in small 

 quantities into a cat until the animal was profoundly insensible, failed 

 to have any effect on the knee jerk. 3 grammes of water containing 

 0*075 gramme of the hydrochlorate of morphia, injected into a r-abbit 

 in the same way, caused exaggeration of the knee jerk, the animal 

 being in a state of torpor with diminished respiration. The third 

 series of experiments were also original, and consisted in compress- 

 ing the abdominal aorta, and thus producing anasmia of the cord, and 

 observing the effect of this on the knee jerk. Such compression, 

 whether employed through the integument or applied directly 

 to the abdominal aorta, in the rabbit caused in a few seconds 

 exaggeration, and then abolition of the knee jerk in about 45 seconds, 

 as a rule, and it remained absent for from 15 or 20 seconds to one or 

 several minutes, after the compression was left off, before returning. 

 The length of time that it remained absent was found to be directly 

 proportional to the length of time that the compression on the aorta 

 had been kept up ; the longer the compression, the slower was the 

 knee jerk in returning. The results obtained from the various 

 methods of experimentation led Prevost to believe that the knee 

 jerk has a decidedly central origin, and is of the nature of a reflex, 

 also that it is the excitation of the tendon, and not of the skin, which 

 elicits it. He further believed that the contraction of the opposite 

 quadriceps when the tendon of one side is struck pointed to the exist- 

 ence of a crossed reflex. 



Waller and Prevost* soon after performed some experiments in 

 conjunction, which proved this last conjecture to be erroneous. They 

 divided the sciatic, anterior, crural, and posterior roots on one side, 

 and yet did not abolish the crossed movement. Percussion of the 

 tendon on the injured side caused no contraction on that side, but 

 evoked a contraction on the opposite side at least as vigorous as 

 before the injury. From this they concluded that there was no 

 physiological transmission, and therefore no "crossed reflex," but 

 that the result was due to physical diffusion of vibrations. 



Senatorf found that the hemisection of the spinal cord affected 

 the knee jerk on the same side only ; that section or greater dis- 

 turbance of the posterior columns of the lumbar cord, or of the pos- 

 terior horns had no effect on the jerk; and that dividing the lateral 



* ' Rev. Med. de-la Suisse Rcniande.' June, 1881. 



f ' Arch. f. Anat. u. Physiol.,' Phpiol. Abth., 18:0, Heft 8. 



