8i8 THE SPINAL CORD. 



In the spinal frog placed in water warm enough to form a skin 

 stimulus, e.g. 36 C., I have seen co-ordinate swimming, for a short 

 time vigorous and executed with the normal bilateral stroke of the 

 hind-limbs, and with movements of the fore-limbs. But the total 

 co-ordination is distinctly less good than when metencephalon and 

 myelencephalon remain. There is a tendency for the animal to dive 

 deeper and deeper in the water ; this seems due to the sunken position 

 of the head: the loss of the semicircular canals cannot be without 

 importance for this condition. Transection at the calamus almost 

 immediately reduces the latent period for reflex movements of the foot 

 as compared with the period when the section lies close in front of 

 mesencephalon. If the reflex for a particular stimulus have been 

 abolished by post-thalarnic section, it is in a few minutes restored by 

 post-calamic. But, on the other hand, the latency and liminal stimulus 

 for the crossed reflex from one foot to the contralateral are less when 

 transection is just above the calamus than when it is post-brachial, 1 

 indicating some solidarity of the spinal organ as a whole in regard to 

 limb movements. The spinal frog, when placed on its back, does not, 

 as a rule, right itself, though it is said that the lizard and the 

 salamander do; in some spinal frogs, inversion excites very active 

 general movements much more than does any general stimulation of 

 the dorsal skin when the animal is not inverted ; but the inversion is 

 not corrected. It is true that spontaneous movements are not observ- 

 able with anything approaching the number and variety shown by 

 the frog possessed of the lower part of the encephalon. At 

 the same time one does see in the spinal frog from time to time 

 changes of position that are not very clearly related to any detectible 

 stimulus. Volkmann's 2 experiment, namely, the placing of the hind-limb 

 in a posture of extension during the period of spinal shock, with the 

 result that, as the shock is recovered from, the limb is drawn up to the 

 sitting posture, can hardly be cited, as he cited it, in instance of a move- 

 ment without external stimulus. An external stimulus to the muscular 

 sense organs of the limb is legitimately postulable. More "spon- 

 taneous " in character are occasional short fits of crawling, for which an 

 external stimulus is less easy to assign. 3 But the whole question is 

 one of degree rather than of kind, if the definition above offered for 

 spontaneity be accepted in the matter. It is to low forms, and 

 especially to invertebrate, that resort has to be made for salient examples 

 of spontaneity persistent after removal of the cephalic portion of the 

 nervous system. 



That the whole spinal cord presents no markedly greater competence 

 in spontaneity than do mere regions of it, may be because its complete 

 length includes no additional kind of sense organ above those dis- 

 tributed fairly equally throughout the body segments belonging to each 

 of its component lengths. 



In all the various examples in which co-ordinate progression has 

 been observed as a function of spinal animals, the progression is always, 

 in a sense, of one type only, namely, in the direction habitual to the 

 species. The normal insect and Astacus 4 can go backwards as well as 



1 Rosenthal (in frog), Biol. CentralbL, Erlangen, 1881 ; Hallsten, Arch. f. PhysioL, 

 Leipzig, 1886 ; Bickel (in Lacerta), Arch. f. d. ges. PhysioL, Bonn, 1898, Bd. Ixxi. S. 44. 

 2 Miiller, Arch. f. Anat., PhysioL u. wissensch. Med., 1838, S. 17. 



3 Redi, " Opusc.," Venezia, 1742, vol. iii. p. 290. The spinal tortoise crawls. 



4 Foster, Huxley, Ward, Bethe. 



