SPINAL REFLEXES. 839 



irritatively upon the spinal centres " like a mild strychnisation " (Charcot). 1 

 But the spinal exaltation has been shown by experiment to set in before 

 Wallerian degeneration has time to occur, and this fact also excludes as a 

 cause the local spinal hypersemia 2 which undoubtedly accompanies the process 

 of Wallerian degeneration and the subsequent healing in the spinal tissue. 

 The remaining hypothesis (3) is that the ablation removes a nervous centre which 

 under normal conditions constantly restrains these spinal reflexes. But the 

 reflexes become abnormally responsive not only after the loss of the cortex ; 

 early arrest of the development of the brain has the same effect, 3 producing 

 abnormal facility of the spinal reflexes, e.g. in agenesic porencephaly. And 

 there is direct experimental evidence demonstrating that the excitation of the 

 cortex can restrain spinal reflex action. 4 The lowering of cerebral restraint is 

 often well marked, even when the effect of the cerebral lesion on motility 

 is slight or undemonstrable. It may be recalled that some (Marie, Mann 

 (Breslau), Marinesco) regard the pyramidal tract as entirely an inhibito-motor 

 path. 



Even where the nervous system, as in lower vertebrata, possesses 

 110 immediate cortico-spinal tract, removal of the hemispheres neverthe- 

 less augments spinal reactions (Marshall Hall 5 ). Other parts of the 

 brain than the cerebral hemispheres also appear to exert restraint upon 

 spinal reflexes : thus the mesencephalon and metencephalon, as shown 

 by Setschenow's 6 and Albertoni's 7 experiments on the frog and toad. 

 The stimulus whence springs the spinal inhibition by the optic lobes of 

 the frog has been shown to act through the retina. 8 In the dog I have 

 seen a semisection of the posterior part of the bulb enormously increase 

 the spinal reflexes on the same side as the section, e.g. the scratching 

 reflex from the trunk and limbs. 



Removal of the " cerebral " ganglia in invertebrata gives to the spinal arcs 

 striking release from restraint. Of the halves of the transected Hirudo or 

 Planarian the hinder crawls the more restlessly. 9 After " decerebration," the 

 cephalopod Eledone enters into ceaseless motor activity, 10 Dytiscus " executes 

 swimming with great energy and rapidity, striking all its comrades to one side 

 by its violence." n Limulus 12 and Astacus 13 constantly execute movements of 

 preening and swinging with their limbs. The removal of restraint occurs on 

 the homonymous side after unilateral lesion in these forms ; the effect is in so 

 far like the extensor spasm supervening when one half of the mesencephalon 

 is transected in the mammal. 14 



The condition of one part of the cord influences the reactions of the other 

 parts. In this respect its homogeneity may be likened to that of the retina 

 (simultaneous induction). Vulpian, on a priori grounds, argued, in his 



1 See also Vulpian, " Le9ons sur les maladies du systeme nerveux," Paris, 1886 ; M. Lion, 

 Ztschr.f. klin. Med., Berlin, Bd. ii. S. 310. 



2 Erben, Wien. med. Wchnschr., 1890, S. 879. 



3 F. Schultze, "Beitrag z. Lehre v. d. angebor. Hirndefecten," Heidelberg, 1886; G. 

 Anton, "Medic. Schriften," herausgegeb. a. d. Wien. klin. Wchnschr., No. xv., 1890; 

 J. Arnold, Bcitr. z. path. Anat. u. z. allg. Path., Jena, Bd. xi. S. 407. 



4 Simonoff, loc. cit.; Bubnoff u. Heidenhain, Arch. f. d. ges. PhysioL, Bonn, 1881, 

 Bd. xxvi. S. 137 ; S. Exner, ibid., 1882, Bd. xxviii. S. 487. 



5 " Memoirs," London, 1838. 



6 "PhysioL Studien ueber d. Hemmungsmechanismen f. d. Refl.," Berlin, 1863. 



7 Arch. ital. de MoL, Turin, 1887, tomo ix. p. 19. 



8 Langendorff, Arch.f. PhysioL, Leipzig, 1877, SS. 95 and 435. 



9 Loeb, Arch.f. d. ges. PhysioL, Bonn, 1894, Bd. Ivi. 



10 v. Uexkiill, Ztschr.f. Biol., 1895, Bd. xxxvi. 



11 Carpenter, "General and Comparative Physiology," third edition, London, 1851. 



12 Ida Hyde (Loeb's laboratory), Journ. MorphoL, Boston, 1894, vol. ix. 



13 Ward, Journ. PhysioL, Cambridge and London, 1879, vol. ii. 



14 Sherrington, Phil. Trans., London, 1897. 



