Chap, viii.] OF THE MODIFYING AGENTS OF NUTRITION. 151 



accustomed to a more abundant nourishment, and if this fails, 

 it becomes inflamed and suppurates.^ 



That paralysis of the capillary vessels, and consequently their 

 persistent dilatation, occasions an excessive afflux of sanguineous 

 plasma, is proved by the following experiments of Professor 

 Schiff. He cut one of the lower maxillary nerves of a mam- 

 miferous animal; then, at the end of a certain time, having 

 killed the animal, he discovered an increase of volume in the 

 bone of the jaw, with rarefaction of the osseous tissue. 



In a dog two months old, the same physiologist cut the two 

 principal nerves of one of the posterior members, the sciatic and 

 crural nerves. Four months afterwards the bones of the member 

 were hypertrophied, and new osseous productions had formed in 

 the foot. This result is due to the section and consequent 

 paralysis of the nervous vaso-motory fibres intermixed with the 

 other fibres of the nerve. 



The same experimentalist has also observed paralysis of the 

 vaso-motory fibres of the ear of a rabbit cause abundance of 

 hairs to grow upon that ear. 



B. The exterior medium also powerfully influences nutrition 

 by its principal physical modalities, especially by light and heat. 



Doubtless, light has not that primordial importance for animals 

 that it has for chlorophyllian plants. The animal kingdom has 

 representatives at the bottom of the Atlantic, at a depth of 

 nearly two kilometres, whither a solar ray never penetrates, but 

 there it is only represented by inferior animals. Nevertheless, 

 in the fauna of caverns, vertebrated species are found ; but they 

 are modified, and modified for the worse, by the absence of light. 

 Very commonly, the organs of sight are atrophied. Besides, 

 very frequently, the skin of the animals of caverns is destitute 

 of the colouring pigment, as has been observed in a blind fish of 

 the cavern of the.Karstgebirge, and in the proteus anguinus of 

 the Mammoth Cave.^ 



^ CI. Bernard, Rapport sur les Progris de la Physiologie 66n6raU, p. 215. 

 ' Leydig, Histiologie Comparie, p. 94, 95. 



