150 BIOLOGY. [BOOK n. 



upon others devolves the task of relieving the animal organism 

 of the non-volatile residue of denutrition, &c. 



But in order that the action, the utility, of these varied or- 

 ganic mechanisms, their influence on nutrition, may be thoroughly 

 comprehended, it is first of all necessary to describe them, which 

 shall be done in its place. We only wish to point out here, in 

 passing, some interesting facts relative to the influence of the 

 nerves and nervous system upon nutrition ; for it would be 

 difficult to place these facts elsewhere. 



It is certain that nutrition is, to some extent, independent of 

 the nervous system. In effect, we see it in operation in the 

 plants, in the lower animals, destitute of a nervous system, and 

 in the embryo, which, as yet, has none. 



Professor Schiff has seen absorption carried on by the 

 stomachal mucous membrane, after the section of nearly all 

 the nerves which communicate with the stomach 1 (solar plexus 

 destroyed, section of the threads of the pneumo-gastric nerve 

 which are joined to the O3sophagus). 



Claude Bernard has likewise observed that the section of the 

 nerves in the wing of a pigeon does not prevent the feathers 

 from shooting. 



But there are very curious contradictory facts. "We shall see 

 farther on that the expenditure, the afflux of blood in the finest 

 sanguineous canalicules, the capillary vessels, is regulated by the 

 influence of certain special nervous threads, called for this reason 

 vaso-motors. Under the influence of these nerves, the capillary 

 vessels contract or dilate ; now these vessels form a net-work of 

 meshes more or less compact in the web of nearly the whole of 

 the organs and tissues, and the afflux of the nutritive sanguineous 

 plasma is more or less abundant, according as their calibre 

 enlarges or contracts. Here then, the influence of the nerves is 

 necessary. Moreover, if we paralyze, by section, the vaso-motory 

 nerves of an organ, we see that this organ can no longer support 

 abstinence as easily as the others. It seems that it may become 

 1 M. Schiff, Lefons sur la Physiologic de la Digestion, 1867, t. ii. p. 404. 



