584 FUNCTIONS OF TOE CEREBRO-SPIN AL NERVOUS SYSTEM. 



same law will be found to prevail in the former as in the latter case, namely, 

 that the points nearer the surface are positive to those nearer the centre. 

 There is no difference between the motor and the sensory nerves in regard 

 to the direction of this current, the existence of which has been proved by 

 M. Du Bois-Reymond, not only by the galvanometer, but also by the excite- 

 ment of contractions in the limb of the galvanoscopic frog. The " nervous 

 current," like the muscular, must be considered as derived from the electro- 

 motive action of the molecules of the nerve; and it seems quite unquestion- 

 able, that every integral particle of the nervous substance must be a centre 

 of electro-motor action, and must contain within itself positive and negative 

 elements; and the variations both of intensity and direction in the nervous 

 current, under certain circumstances, are so sudden and so extensive, that it 

 appears impossible to account for them by any change of larger heteroge- 

 neous elements, or in any other way than by assuming corresponding changes 

 of position in almost infinitely small centres of action. It is indifferent what 

 form is assigned to these electro-motive molecules ; but it would seem that 

 they must have two negative polar zones, and a positive equatorial zone; a 

 combination of such elements being able to produce all the electrical effects 

 of a nerve in a state of rest. It seems altogether best to suit the phenomena, 

 to suppose that each of these peripolar molecules is formed by the combina- 

 tion of two dipolar molecules, touching each other by their positive poles, 

 as in the subjoined table, which represents a baud of four series, A, B, c, D, 

 each series containing four dipolar molecules: 



A.. 

 B.. 

 c., 



D, 



The relative position of these sets of molecules may, however, under certain . 

 circumstances, be changed ; and the very remarkable modification of the 

 "nervous current," which has been shown by JVJ. du Bois-Reymond to 

 follow severe injuries of the nerve by mechanical, chemical, or thermal 

 agencies, appears to be attributable to such an alteration. If, for instance, 

 a piece of hot metal be brought near to the nerve without touching it, the 

 nervous current will be seen to diminish rapidly, and to have its direction 

 reversed, during which the property possessed by the nerve of conveying 

 irritation to the muscle, though somewhat impaired, will not be destroyed ; 

 and if, whilst in this abnormal state the nerve be divided, every transverse 

 section is found neutral or positive to the longitudinal section, instead of 

 negative. If the nerve-trunk be then placed between muscles, so as to re- 

 cover its natural moisture, it will at the same time recover its usual electro- 

 motive power. The same phenomenon is often exhibited in winter, when 

 the frogs serving for experiment have been exposed to cold. The muscle or 

 nerve is thru said to present a " parelectronomic" behavior, and Du Bois- 

 R;'V;nnnd explains it by assuming that in the case of muscle there is a layer 

 of muscle in contact with the tendon which acts electro-motorially in an op- 

 posite direction, and this equals, or even over-compensates, the normal cur- 

 rent. To represent this parelectronomic layer, it is only requisite to take 

 away the ultimate molecule of 'the dipolar molecule, when the last one will 

 turn its positive side to the surface. According to M. Du Bois-Reymond, 

 the ciu-rmt shown by the entire nerve, when made to form part of a circuit, 

 is only a dcrioc-d current produced by incomparably more intense currents 

 circulating in the interior of the nerve around these ultimate particles, vary- 

 ing greatly in intensity according to the mode in which these particles are 



