ELECTRICAL PHENOMENA IN NERVE AND MUSCLE. 



583 



in which the term "Physiological time" signifies the period occupied in the 

 perception of the impression, and in the origination of the motor impulse and 

 execution of the muscular movement by which the time was registered. 



Thus it will be observed that the perception and registration of an unex- 

 pected appearance (spark) occupies much more time than the perception of 

 a slowly-awaited one (transit observation), and one-third more than even 

 the perception of a sound ; but the mean variation in the latter case is con- 

 siderably greater. The value of such experiments in affording information 

 respecting the rapidity of conduction of sensory nerves is, however, but 

 small, since the total or physiological time occupied includes: 1. The time 

 required for the reception of the sensation at the integument. 2. The time 

 required for its transmission through the sensory nerve. 3. The conversion 

 of the sensory impulse into a motor impulse. 4. The transmission of this 

 impulse through the motor nerve, and lastly, the execution of the muscular 

 contraction, each of which events may occupy a variable time. 



472. Electrical Phenomena in Nerve and Muscle. The electrical phenom- 

 ena presented by the nerves and muscles are in many respects so similar 

 that it will prevent repetition if they are here considered together. 1 When 

 u small piece of a nerve-trunk or a cylindrical or fusiform muscle is cut out 

 from the recently killed body, and is so placed upon the electrodes of a 

 Galvanometer that it touches one of them 

 with its surface (or natural longitudinal sec- 

 tion), and the other with its cut extremity 

 (or artificial transverse section), a considera- 

 ble deflection of the index is produced, the 

 direction of which always indicates the pas- 

 sage of a current from the interior to the 

 exterior of the nerve-trunk, or from the lon- 



Fio. 19.5. 



gitudinal section 



and galvanometer 



through the galvanometer 



This figure is intended to show th<? di- 

 rection of the currents in a columnar 

 portion of nerve or muscle. L, longi- 

 tudinal section: Q. transverse section 

 a 6, the equator. The barbed lines in- 

 dicate the direction, and their thickness 

 the force of the currents established, 

 where the electrodes of a galvanometer 

 are applied to the corresponding sur- 

 faces. The dotted lines show inopera- 

 tive arrangement;. 



wire and galvanometer to the transverse 

 'section. This is shown diagrammatically in 

 Fig. 195. It is indifferent in regard to the 

 direction of the current, "whether the central 

 or the peripheral cut extremity be applied 

 to the electrode ; and in fact the most power- 

 ful effect is obtained by doubling the nerve 

 in the middle, and applying both transverse 

 sections to one electrode, whilst the loop is 

 applied to the other. On the other hand, if 

 the two cut extremities be applied to the two 

 electrodes respectively, no decided effect is 

 produced ; and the same neutrality exists 

 between any two points of the surface of the trunk, equidistant from the 

 middle of its length or equator (a b, Fig. 195) ; but if the points be not equi- 

 distant, then a deflection is produced, indicating that the parts nearer the 

 middle are positive to those nearer the extremities. It has not been found 

 possible, owing to the small size of the nerve-trunks experimented on, to test 

 in a similar manner the relative state of different points of their transverse 

 section ; but there can be little doubt, from the complete conformity which 

 exists in other respects between the nervous and muscular currents, that the 



1 The principal works to be consulted on this subject are Du Bois-Reymond, Un- 

 tersnchungen iiber thierische Electricitiit, in which a complete list of all previous 

 wc'fks is contained ; Wtindt, Untersuchungen zur mechanik cler Nervon und Nerven 

 centren, 1871 ; Munk, Hermann, Pfliiovr, and others, in Pflu^er's Archiv f. gesammte 

 Physiolog., 1868-1875; Oniinus, Archives de Physiologic, 1874. 



