CENTRAL NERVOUS SYSTEM. 213 



brain does not deprive a ray (Torpedo oculata) of the power of perfect loco- 

 motion. The same is true of the ganoid fish. In the case of the cyclostome 

 fish (Petromyzon) the beheaded trunk is, in the water, inactive, yet, on gentle 

 mechanical stimulation, it makes inco-ordinated responses ; but, put in a bath 

 formed by a 3 per cent, solution of picro-sulphuric acid, locomotion under 

 the influence of this strong and extensive dermal stimulus is completely per- 

 formed. In the case of the eel the responsiveness even to the picro-sulphuric 

 acid bath is evident in the caudal part of the body alone. 1 n the bony fish this 

 capability of the spinal cord to control locomotion has not been observed. 1 



In these experiments the central system is represented by the entire spinal 

 cord with the associated nerves, or by some fraction of it; but so simple, 

 constant, and independent are the reactions of the cord under normal condi- 

 tions that a strong stimulus is able to elicit the characteristic responses from 

 even a fragment of the system. The higher Ave ascend in the vertebrate 

 series the less evident do the independent powers of the cord become. 



Tarchanow 2 has shown that beheaded ducks can still swim and fly in a 

 co-ordinated manner, and among mammals (dog and rabbit) Goltz and Ewald 3 

 and others have demonstrated that if the lumbar region be separated from the 

 rest of the cord by a cut and the animal allowed to recover from the opera- 

 tion it will with proper care live for many months, and not only are the legs 

 responsive to stimulation of the skin, but the reflexes of defecation and urina- 

 tion are easily induced by slight extra stimulation. An instructive reaction 

 occurs when such an animal is held up so that the hind legs hang free. 

 When thus held, the legs slowly extend by their own weight and then are 

 flexed together. The reaction becomes rhythmic and may continue for a long 

 time. It is assumed in this case that the stretching of the skin and tendons 

 due to the weight of the pendent legs acts as a stimulus, and in consequence 

 the legs are flexed. This act in turn removes the stimulus, and as a result 

 they extend again, to be once more stimulated and drawn up. 



In man, as a rule, death rapidly follows the complete separation of any 

 considerable portion of the cord from the rest of the central system, especially 

 if the separation be sudden, as in the case of a wound. But Gerhardt 4 has 

 recorded the retention of the reflexes in a case of compression of the cord by 

 a tumor, the case having been under observation for four and a half years ; 

 and Hitzig, 5 a case in which a total separation between the last cervical and 

 first thoracic segments had been survived for as long as seven years. The 

 principal reaction to be observed in such cases is a contraction of the limb 

 muscles in response to stimulation of the skin, such as a drawing up of the 

 legs when the soles of the feet are tickled. No elaborate reflexes are, how- 

 ever, retained such as would be necessary in acts of locomotion. 



1 Steiner : Die Functional des Centralnervensystems mul ihre Phylogeneae, 2te Aluli., "Die 

 Fische," 1888. 



2 Tarchanow : Pfl.ugei?8 Archiv, 1885, I'd xxxiii. 



3 Goltz und Ewald : Ibid., 1896, Bd. lxiii. 



4 Neurologisches Centrcdblatt, 1894, 8. 502. ' Loc. cit. 



