STRUCTURE OF THE SPINAL CORD. 597 



The natural electrical state of nerve and muscle during the state of rest, according 

 to Dr. Radcliflv, is one in which the fibres are electro-motive elements in the state of 

 open circuit, the coats being charged positively, and the contents negatively l>v <],<- 

 tro-motive action. While charged in this manner the condition of the muscle is that 

 of relaxation or elongation; when this charge is discharged contraction is the result; 

 and the broad conclusion is that the state of relaxation or elongation is consequent 

 upon the presence, just as the opposite state of contraction is consequent upon the ab- 

 sence of this charge, the charge operating by setting up a state of mutual repulsion 

 among the muscular molecules, the discharge doing its work by allowing the attrac- 

 tion force or forces inherent in the physical constitution of the molecules to come into 

 play. Hence it is not altogether unintelligible that the artificial charge belonging to 

 the electrotonic states may set up a state of muscular elongation which is greater than 

 that which is natural to the muscle, for the simple reason that the artificial charge is 

 greater than the natural charge, and that it may at the same time act like the natural 

 charge in uihihiUng contraction. Hence the exaggeration of tetanus in cathelectro- 

 tonus may be not altogether unintelligible, for if contraction is only the passive re- 

 turn from a previous state of elongation consequent upon charge, it follows that the 

 contraction in electrotonus may be greater than that which is natural to the muscle, 

 for the simple reason that there is in electrotonus a greater degree of elongation be- 

 foiv the contraction than that which is natural to the muscle. And hence, too, the 

 explanation of the fact, that contraction is inhibited more effectually by anelectro- 

 tomis than by cathelectrotonus, and that the contraction on closing and opening the 

 circuit continues for a longer time under anelectrotonus than under cathelectrotonus, 

 for these differences after all may be nothing more than the natural consequence of 

 the way in which the action of the artificial charge agrees with that of the natural 

 charge in the one case, and disagrees in the other, the -f- artificial charge imparted 

 to the outsides of the fibres in anelectrotonus agreeing with the -(- charge which is 

 natural to these parts, and so favoring the continuance of that natural state of charge 

 which at once inhibits contraction and allows of contraction; the artificial charge 

 imparted to the outsides of the fibres in cathelectrotonus disagreeing with the '4- 

 charge which is natural to these parts, and being, on this account, unfavorable to the 

 continuance of that natural state of charge which at once counteracts contraction and 

 makes contraction a possibility. In a word, the explanation of the longer or shorter 

 continuance of the contraction which happens in this case in the closing and opening 

 of the circuit is the same as that which Dr. Radcliffe applies to the explanation of 

 the longer or shorter continuance of the same contraction under the "inverse" and 

 11 direct" currents; for in this latter case the evidence goes to show that the differences 

 in question have to do, not with differences in the direction of the current, but with 

 differences in the charge associated with the current, the + charge associated with 

 the " inverse " current being favorable to the continuance of the contraction, the 

 charge associated with the "direct" current being unfavorable. 



2. Of the Spinal Cord and Medulla Oblongata; their Structure and Actions. 



479. In our more detailed consideration of the functions of the several 

 divisions of the Nervous System, it is desirable, for several reasons, to com- 

 mence with the Cranio-splnal Axis; which, as already pointed out, may be 

 considered as constituting the fundamental portion of this apparatus. The 

 entire Axis is divided into its Cranial and its Spinal portions, the passage of 

 the Cord through the " foramen magnum " of the occipital bone being con- 

 sidered to mark the boundary between them ; and although the separation 

 of the Medulla Spiualis from the Medulla Oblongata, which is thus estab- 

 lished, is in itself purely artificial, yet it will be found to correspond com- 

 pletely with the natural division founded on their respective physiological 

 attributes. 



480. The Spinal Cord, 1 which extends from the margin of the foramen 



1 The sketch given in the text of the Anatomy of the Spinal Cord, is chiefly de- 

 rived from the statements of Prof. Kb'lliker, in his Mikroskopische Anatomic (Bd. 

 ii, H 115, 116), and of Mr. J. L. Clarke, in the Philosophical Transactions, 1851, 

 1853, and 1859 ; but Gerlach gives an excellent account of it in Strieker's Hum. and 

 Comp. Histology, Syd. Soc. Transl., vol. ii, p. 327. 



