8 7 2 



THE SPINAL CORD. 



A great interest attaches to the knee-jerk and similar reactions as indices 

 of the condition of the nervous system. Extinguished when the neural tonus 

 of the muscle is extinguished (e.g. by complete rupture of the reflex arc) or is 

 replaced by the active innervation of intentional movement, these "jerk" 

 phenomena are indicators delicate enough to show many shades of spinal state. 

 Under apparently like circumstances, there are, in any large collection of 



healthy individuals, not in- 

 considerable differences of 

 knee-jerk. In a very few 

 persons, apparently healthy, 

 the knee-jerk is at times 

 inelici table 1 even under most 

 favourable conditions. Of 

 alterations in the jerk, some 

 are referable to conditions 

 directly affecting the local 

 reflex arc itself. Thus, a 

 second tap given soon after 

 a first will generally evoke a 

 more ample jerk. 2 A series 

 ^VASTUS CRUREUS of taps too feeble to singly 

 is evoke the jerk, will, when 

 repeated at intervals from a 

 fifth to a tenth of a second, 

 become efficient. Conversely, 

 after the jerk has been 

 elicited for a number of 

 times, it tends to fail for a 



, short period, despite the 

 FIG. 3o9. Scheme of the arrangement of the nerves and , \ ' . 



muscles of chief importance in the knee-jerk, as ta P s bem g continue 

 determined in the Macaque monkey. The numbers fore. Local fatigue of the 

 4L-8L indicate the post-thoracic spinal roots of extensor muscles diminishes 

 Motacus, and the numbers in brackets the corre- ^ ie ^ . 3 g ene ral fatigue of 

 spending lumbar and sacral roots of man. The . J 



arrows pointing to the right indicate efferent paths, the nervous system at first 

 those pointing to the left afferent paths. increases, but if severe, later 



diminishes the jerk. The 



rendering of the limb bloodless by the Esmarch bandage causes the knee-jerk 

 in about fifteen minutes to disappear. 5 "Pathic" stimuli 6 applied to the 

 skin increase the jerk, and friction of the skin of the leg, 7 and the cold 

 bath 8 , are means of increasing the jerk in patients in whom it is defective. 



1881 ; Schreiber, Arch. f. exper. Path. u. Phannakol.. Leipzig, 1885, Bd. xviii. S. 270 ; 

 Sherrington, Proc. Roy. Soc. London, 1892, vol. li. ; Schultze and Fitrbringer, Centralbl. 

 f. d. med. Wissensch., Berlin, 1875, S. 929. 



1 Eulenberg without the now known reinforcements failed to elicit the jerk in sixteen 

 out of 238 healthy children ; Pelizseus and Remak with use of reinforcements found the 

 jerk present in each of 2403 healthy children examined in succession, Arch. f. Psychiat., 

 Berlin, 1885, Bd. xiv. S. 402 and 167. 



2 Heller, JBerl. klin. Wchnschr., 1886, S. 903; Meyer, ibid., 1888, S. 23; Schreiber, 

 loc. cit. 



3 Muhr, Centralbl. f. Nervenh. u. Psychiat., Coblenz u. Leipzig, 1878 ; Jendrassik, Deutsches 

 Arch. f. klin. Med., Leipzig, Bd. xxxiii. S. 177 ; Eisenlohr, Festschr. f. Eroffn. d. neu 

 allgem. Krankcnh. z. Hamb. Eppendorf., 1889 ; Sternberg, "Sehnenreflexen," Wien, 1893. 



4 Brissaud, op. cit. ; Marmian, Riv. din. di Bologna, 1884, p. 415; Schuster, "Diagnostik 

 d. Ruckenmarkskrankheiten," Berlin, 1884; Erlenmeyer, "Ueber statischeReflexkrampfe," 

 Leipzig, 1885 ; Sternberg, Centralbl. f. Physiol., Leipzig u. Wien, 1887, Bd. i. S. 81. 



5 Sternberg, "Die Sehnenreflexen," Wien, 1893, S. 69. 



6 Weir Mitchell and Lewis, Med. News, Phila., 1886; Jarisch u. Schiff, Med. Jahrb., 

 Wien, 1882. 



7 Schreiber, op. cit. 8 Dunge, "Diss.," Bonn, 1889. 



