582 FUNCTIONS OF THE CEREBRO -SPIN AL NERVOUS SYSTEM. 



intervened from the instant of the application of the stimulus to the nerve 

 at a, to the moment when the contraction of the muscle breaks that current. 

 A portion of this time, is occupied in the transmission of the stimulus from 

 the point a to the muscle, and a portion, termed the period of latent excita- 

 tion, elapses before the muscle responds to the stimulus. In order to ascer- 

 tain the duration of the former period, the experiment is repeated with this 

 alteration, that the stimulus is applied at b, and again the extent to which 

 the needle is deflected is read off; the difference between the two observa- 

 tions then gives the time occupied. by the stimulus in passing from a to 6. 

 From numerous experiments with this instrument, Helmholtz arrived at the 

 conclusion that in the Frog, at a temperature between 52 F. and TCP F., 

 the rapidity of the propagation of impressions along motor nerves was from 

 81 to 126 feet per second, and he estimates the rapidity for human nerve at 

 somewhat more than 200 feet per second. 1 Other observers have obtained 

 the following results: Hirsch,' 2 34 metres (111. 5 feet); and Schelske, 3 29.6 

 metres (98.4 feet) per second in the Frog. Marey, 4 from 12 to 15 metres 

 (36 to 48 feet) per second in the same animal in winter. Bonders and De 

 Jaager, 5 26.09 metres (88 feet) for the sensory nerves of Man. And Kohl- 

 rausch 6 also from experiments on Man, at 94 metres (308.3 feet) per second. 

 Still more recently Helmholtz, 7 in experiments conducted with Herr Baxt, 

 obtained the number 33.905 (111.22 feet) for Man, whilst Place and Van 

 West 8 found that the mean velocity in man was 53 metres (174 feet) per 

 second. In these experiments as well as in those of Munk it was found that 

 the rapidity of transmission is greater in the peripheral than in the more 

 centrally situated portions of the nervous system. [Bloch states that the ra- 

 pidity of the sensory current in man is, for the cord, 194 metres per second, 

 and for the nerves 132 metres per second.] 9 Colin 10 has noticed that if the 

 sympathetic ganglia are strongly irritated, reflex movements are immediately 

 produced ; but when the excitation is more feeble, a longer time elapses be- 

 fore the movements occur. M. Hirsch has even attempted to determine the 

 relative rapidity with which impressions are transmitted through the nerves 

 of sight, hearing, and touch ; and the following table gives his conclusions, 



1 According to Troitzky, with feeble currents the maximum velocity of propaga- 

 tion is between 50 and 68 Fahr., the, rapidity being greatly reduced when the nerve 

 (in the Frog) is warmed to 86 or cooled to Fahr. With strong currents the in- 

 fluence of the temperature upon the conductivity of the nerves diminishes or becomes 

 altogether imperceptible (Pfliiger's Archiv, Bd. viii, Heft xii). Both these experi- 

 ments and the antecedent ones of HelmholU and Baxt (Monatsberieht d Berlin 

 Acad., 1870, p. 184) show that the influence of temperature must not be overlooked 

 in examining the conductivity of nerves. 



2 Moleschott's Untersuch.,'Bd. ix, 1863, p. 183. 



s Kcichert's Archiv, 1864, p. 151. * Gaz. Med. de Paris, 1866, p. 124. 



* Nederlandsch. Archief, Bd. i, p. 518. 



8 H.-nle, Pfcutter's Z"Hs., Bd. xxviii, 1806, p. 190. 



' B.-richte der Berliner Akad.-m., 18G7, p. 229. ' Pfliiger's Archiv, Bd. iii, p. 424. 



[Chicago Journal of Mental Diseases, vol. ii.] 



Comptes Kcndus, 18I11, torn, i, p. 9(19. 



Ber. d. k. Sachs. Gesell. der Wiss., Feb. 1866. 



