793 THE SPINAL CORD. 



conduction in the direction from dorsal root to ventral root, but not 

 conversely. This is the special case which gave the foundation of the 

 law of conduction in the neural system termed the "law of forward 

 direction," which has been already referred to (p. 785). 1 



The practically universal spinal irradiation obtained under strychnia bore 

 out the view of a conducting network continuous in all directions throughout 

 the grey matter. But when the property of "double-conduction" by nerve 

 fibres had been ascertained, the " Bell-Magendie law " of the roots became more 

 instructive. Since the dendritic processes of the efferent root cells join the 

 general network, the Bell-Magendie law must indicate either that these 

 dendrons are non-conductive, or that they, although conductive from the 

 network into the motor cell, are not conductive back from the motor cell into 

 the network. Gad (1884) 2 especially insisted on the latter view; Golgi 

 (1882) 3 on the former, considering the dendritic processes to be simply nutrient. 

 Since the recent more general rejection of the theory of a continuous intra- 

 spinal network, Cajal (1889) and van Gehuchten (1891) 4 have argued a 

 " dynamical polarisation " of the nerve cell so that the sense of conduction 

 is solely from dendron toward axon, never the reverse. They suggest the 

 importance in this connection of the " articulation " between axon of one 

 cell and dendron of next. The " valved " condition of the circuits may 

 result from properties belonging to these places of " contact utile " or 

 "synapse." The "dynamic polarisation" of the cell seems to find expres- 

 sion in certain morphological characters of the cell, so that the two ends 

 are in many cases recognisable by inspection. In accord with the constant 

 failure to provoke reflex actions or signs of sensation by stimulation on the 

 proximal side of the transection of an efferent spinal root, all attempts 5 to 

 similarly provoke from that root action currents in other nerve tracts have 

 failed. 



An immediate influence exerted by the efferent root cells on the 

 motor root cells, as indicated by the skeletal muscles, is demonstrable in 

 various ways. The posture of the hind-limb of the spinal frog, when 

 the limbs are allowed to hang freely (Brondgeest's phenomenon), 6 shows 

 that the lengths of the flexor muscles of the limb are, under those 

 conditions, slightly shorter than when the afferent roots of the sciatic 

 plexus have been severed. Early experiments failed 7 to show any 

 lengthening of the muscles on section of their nerves, but the muscles 

 were examined after arrest of the circulation and under extension by 

 not inconsiderable weights. With lighter weight and intact circulation 

 Wundt 8 observed a lengthening after section of the muscular nerves, 

 but, confronted by a somewhat similar lengthening, resulting as an after- 

 effect of simple contraction of the muscle, he hesitated to accept the 

 lengthening consequent on nerve section as due to anything more than 



1 See W. James, loc. cit., Boston, 1880 ; see also J. Midler's " Handbuch," 1834, 

 Bd. i. Abth. 2. 



2 Tagebl. d. 66<e Vcrsamml. deutsch. Naturf. u. Aerzte; " Eulenberg's Real-encvc," 1888, 

 Bd. xvi. S. 673. 



s "Studi istolog.," Milano, 1881; Gior. intcmaz. d. sc. med., Napoli, 1881, 

 tomo iii. 



4 Cellule, Lierre et Lou vain, fasc. 1. 



5 Hermann, "Lehrb. d. Physiol.," Aufl. xi. S. 6; Gotch and Horsley, Phil. Trans., 

 London, 1891; Mislawski, Compt. rend. Soc. de biol., Paris, 1894, p. 488; Bernstein, 

 Arch. f. d. ges. Physiol., Bonn, Bd. lxxiii. 



6 Holland. Beitr. zu d. anat. u. physiol. Wissensch., Dhsseldorf, 1860. 



7 R. Heidenhain, "Physiol. Studien," Berlin, 1856. This work contains full references 

 to all the previous literature. 



8 " Lehre v. d. Muskelbewegung, " Braunschweig, 1858. 



