40 



appear altered, although there is a very material change in this 

 substance when it coagulates. 



2. If such a change as that which takes place in this sub- 

 stance when it coagulates, existed in a part possessing the vital 

 properties belonging to nerves, there should certainly be a 

 movement or a sensation accompanying it, and yet there is none. 

 This material change is certainly more considerable than the 

 change effected by a slight mechanical or galvanic excitation, 

 which is capable of producing a movement or a sensation. 



3. The microscope has already proved that the white sub- 

 stance does not exist in all the nerve-fibres, and that it is want- 

 ing, for instance, in the very fine fibres. 



Therefore if it be not the white substance of Schwann which 

 is active in the nerves, and as it is not the cylinder axis which 

 possesses the vital properties of the nerves, because it is wanting 

 in many fibres, it results that it is the membranous layer, the 

 paries of the nerve-tube, to which these vital properties belong, 

 unless there is another substance, still unknown, and existing in 

 the tubular canal of the nerve-fibre. 



XVI ON THE PERSISTENCE OF LIFE IN ANIMALS DEPRIVED OF 



THEIR MEDULLA OBLONGATA.* 



I. There is no part in the nervous system considered as more 

 essential to life than the medulla oblongata. In the last few years 

 many German physiologists have asserted that this nervous 

 centre is the source of the rhythmical movements of the heart. 

 Besides, an eminent physiologist maintains that in the medulla 

 oblongata a small part exists which is the focus of vital power. 

 Moreover, it is certain that the medulla oblongata has a great 

 share in the respiratory movements. Therefore it seemed pro- 

 bable that the ablation of such an organ, even in cold-blooded 

 animals, ought to be speedily followed by death. Such is not, 

 however, the result of that operation ; and in favorable condi- 

 tions, the batrachia, for instance, can live more than four 

 months after the loss of the medulla oblongata. During all that 

 time, these animals, in appearance remain in good health, and I 

 have observed in them the existence of all the following func- 

 tions and properties : 



* See the Bulletin de la Soc. Philomatique. Paris, 1849, p. 117. 



