438 Mr. J. S. R. Russell. Circumstances under wh ich [May 18, 



column at the level of the 5th to the 6th lnrabar vertebrae augmented 

 the jerk on that side. 



The latest experimental work on the subject is that by Sherring- 

 ton,* who found that section of those branches of the anterior crural 

 which supplied the vastus internus and adjoining part of the crureus 

 abolished the knee jerk, while when these branches were left intact, 

 and all the other branches of the nerve divided, the knee jerk 

 remained active. He also noted that section of the 6th roots in 

 rabbits did not always abolish the knee jerk, but occasionally section 

 of the 5th root alone sufficed to bring about this result. In the cat, 

 this observer found that when all the anterior and posterior nerve 

 roots of the lumbo-sacral region, with the exception of the 6th, were 

 divided, the knee jerk became brisk ; but that section of the 6th root 

 instantly abolished the jerk. When only half the filaments which 

 composed the posterior root of the 6th root were alone divided the 

 knee jerk was at once extinguished. Section of the anterior root of 

 the 6th root greatly diminished, but did not absolutely abolish, the 

 jerk ; when, however, the ventral root of the fifth was subsequently 

 divided in the same animal the knee jerk was abolished. In llacacus 

 rhesus division of the 5th root never failed to abolish the knee jerk, 

 while section of all other adjacent roots only tended to render it more 

 brisk. Section of the whole, or even half, of the posterior root of 

 the 5th abolished the knee jerk ; but when the efferent root of the 

 5th was divided a remnant of the jerk persisted, as long as the 

 efferent root of the 4th lumbar was left intact. Bisection of the 

 cord in the lumbo-sacral region of JIacacus rhesus produced no altera- 

 tion in the knee jerk. Transverse section of the cord at the level of 

 the 9th thoracic root caused the knee jerk to disappear ten minutes 

 later, and it did not commence to return until three weeks after. A 

 similar lesion of the cord at the level of the 1st lumbar root, with 

 partial section at the 3rd lumbar, caused abolition of the jerk, and 

 it did not return during the six months that the animal was under 

 observation. When the knee jerk was abolished by the inhalation of 

 chloroform it did not return so rapidly when the cord had been pre- 

 viously divided transversely as when it was left intact. „ 



In a later paperf Sherrington has greatly added to our knowledge 

 of the nerve arc on which depends the efficiency of the jerk. After 

 showing how very readily the afferent fibres in the 5th lumbar pos- 

 terior root (Rhesus), and on which the existence of the knee jerk 

 depends, can be impaired, he proceeded to expand the observation of 

 Tschiriew concerning the hamstring nerve, and he then found that 

 excitation of this branch only of the sciatic trunk inhibited the jerk 

 (thus excluding for the most part skin paths), and further that 



* < Journ. of Physiol.,' vol. 13, No. 6, 1892. 

 f ' Koy. Soc. Proc.,' February 9, 1893. 



