RELATION OF AFFERENT TO EFFERENT ROOTS. 799 



the contraction caused by the stimulus when the nerve was cut. Cyon 1 

 and Tschiriew 2 obtained a lengthening after nerve section, the former 

 also after section of the afferent spinal roots ; and both, from their 

 experiments, concluded in favour of a demonstrable reflex slight tonic 

 contraction of muscle, v. Anrep's 3 experiments discriminated between 

 the two instances of lengthening observed by Wundt, and seem to con- 

 clusively establish a reflex tonus of the adductor magnus and semi- 

 membranosus muscles of the frog. Curari breaks the tonus down 

 through the motor-end plate, morphia through the afferent spinal 

 channel. 



Cyon 4 early insisted on the occurrence of a fall in the excitability of the 

 motor root, as tested by faradisation and muscular contraction, ensiling upon 

 severance of the afferent root. Harless 5 had previously stated that the excit- 

 ability of the sciatic nerve of the frog is lowered by section of the afferent 

 spinal roots connected with it. Cyon's facts were disputed, 6 but other 

 observers have confirmed them, 7 and they have been reaffirmed by himself. 8 

 They have been extended to the mammalian roots, 9 and the phenomenon 

 seems well observable after cocainisation or section of the sacral roots of 

 the dog. 



Any interference with the nervous system which paralyses a skeletal 

 muscle delays the onset of rigor mortis in it (Hermann 10 ). Section of the 

 motor spinal roots thus delays onset of the rigor ; and so also does section of 

 afferent roots, 11 even if practised a short time only before destruction of the 

 animal. It also causes some wasting of adult and some interference with 

 growth of young muscles. 12 When a limb has been rendered apsesthetic by 

 severance of all its afferent roots, the muscles feel peculiarly limp and flaccid, 13 

 and the passive mobility of the joints is greater than normal. The same con- 

 dition is met with in many cases of tabes dorsalis ; 14 the hip can, with the 

 limb extended at the knee, be flexed to abnormal extent. This increased passive 

 mobility is due no doubt to loss of tonus (hypotonia) in the limb muscles. At 

 the same time it may be that not all skeletal muscles habitually possess such a 

 tonus, and certain muscles appear at least to possess it in higher degree than 

 others. A slight degree of tension of the muscle is a necessary condition for 

 the elicitation of the knee-jerk, and any damage which breaks the reflex arc 



1 JBer. d. k. sdchs. Gesellsch. d. Wissensch. Math.-phys. CI., Leipzig, 1865. 



2 Arch. f. Physiol., Leipzig, 1879. 



3 Arch./, d. ges. Physiol., Bonn, 1880, Bd. xxi. S. 226. 



4 Op. tit., S. 85. 



5 Abhandl. d. bayr. Alcad. Physik., 1858, Bd. xxxi. 



6 v. Bezold and Uspensky, Centralbl. f. d. vied. Wissensch., Berlin, 1867, S. 611 ; G. 

 Heidenhain, Arb. a. d. physiol. Lab. zu Wiirzburg, 1868, Bd. iii. S. 107. 



7 Guttmann, Centralbl. f. d. med. Wissensch., Berlin, 1867, S. 689 ; Marcacci, Arch, 

 per le sc. med., Torino, 1882, tome v. p. 283. 



8 Steinmann, Bull. Acad. imp. d. sc. de St. Pe'tersbourg, 1871, tome vii. p. 787 ; Cyon, 

 Arch./, d. ges. Physiol., Bonn, 1874, Bd. viii. S. 347. 



9 E Belmondo e R. Oddi, " Intorno all' influenza cette radici spinali posteriori sull 

 eccitabilita della anteriori," Lab. di Fisiol., Florence, 1890. 



10 v. Eiselsberg, Arch. f. d. ges. Physiol., Bonn, Bd. xxiv. S. 229 ; v. Gendre, ibid., Bd. 

 xxxv. S. 45 ; Aust, ibid., Bd. xxxix. S. 241 ; Bierfreund, ibid., Bd. xliii. S. 195 ; J. R. 

 Ewald, ibid., 1894, Bd. liv. ; and Tammassia, Riv. sper. di freniat., Reggio-Emilia, 1882; 

 and Atti. r. 1st. Veneto di sc., lett. ed arti., tome iii. p. vi. 



11 Sherrington, Proc. Roy. Soc. London, 1893, vol. liii. p. 408 ; Mott and Sherrington, 

 ibid., 1895, vol. lvii. p. 481. 



12 Mott and Sherrington, loc. cit. ; H. E. Hering, Neurol. Centralbl., Leipzig, 1897, 

 Bd. xvii. 



13 B. Stilling, Arch. f. physiol. Heilk., Stuttgart, 1842, S. 97 (frog); Mott and Sherring- 

 ton, loc. tit. ; H. E. tiering, Arch. f. exper. Path. u. Pharmakol., Leipzig, 1898, Bd. 

 xxxviii. S. 266. 



14 See, for instance, Jendrassik, Neurol. Centralbl., Leipzig, 1896, No. 17; and Frankel, 

 ibid., 1896, No. 8. 



