392 BIOLOGY. [Book vn't 



on tte arm, a true movement of defence, which projects the hand 

 from the side of the chest to the pit of the stomach. " ^ 



It is assuredly the grey, that is to say cellular substance, 

 which serves as centre to^ these reflex acts : for it is indispensable 

 and it is sufficient that these substances exist, for these reflex 

 actions to be produced. After making almost complete hemi- 

 sections of the marrow Van Deen still obtained reflex actions of 

 the four members. We have seen Professor Schiffi interrupt by 

 many alternate hemisections the continuity of the white sub- 

 stance of the marrow in a cat, wliich did not hinder him from 

 still obtaining contractions of the iris, by pinching the animal's 

 tail. 



As the celebrated experiments of Legallois have demonstrated, 

 the diverse regions of the marrow correspond each to a special 

 region of the body. They have a certain independence, and after 

 a section can live a long time, by retaining their reflex excita- 

 bility, provided their capillary circulation is not fettered. This 

 sort of federation of the diverse regions of the spinal marrow 

 confirms the opinion which regards this nervous centre of the 

 vertebrates as a fusionated ganglionary chain. 



We know moreover that apart from all vivisection, there are 

 in the marrow normal functional centres. Such is the nodus 

 vitalis of the superior vertebrates, that joint some millimetres in 

 thickness, situated at the origin of the marrow, and whose 

 destruction has for result instantaneous death, due to the aboli- 

 tion of the respiratory muscular movements. Such is also the 

 cilio-spinal centre, situated as high as the two first nervous roots 

 of the dorsal marrow, and holding under its empire almost 

 all the capillary circulation of the head. Such finally is the 

 genito-spinal centre, situated in the lumbar region in man. 



Like all the tissues, the nervous tissue only works on condition 



of being fed : also its vitality is intimately dependent on the 



integrity of the sanguineous circulation among its elements. 



But more than all other tissues, it is intermittent in its mode of 



' Ch. Eobin, Journal de PhysUilogie, Paris, 1869. 



